diff --git a/cspell.json b/cspell.json
index 20fda3420..a7fece6ad 100644
--- a/cspell.json
+++ b/cspell.json
@@ -128,7 +128,8 @@
     "CHKSIGNU",
     "CHKSIGNS",
     "RAWRESERVE",
-    "SENDRAWMSG"
+    "SENDRAWMSG",
+    "SDBEGINSQ"
   ],
   "flagWords": [],
   "ignorePaths": [
diff --git a/src/generator/writers/writeFunction.ts b/src/generator/writers/writeFunction.ts
index fd613afeb..cb2727018 100644
--- a/src/generator/writers/writeFunction.ts
+++ b/src/generator/writers/writeFunction.ts
@@ -24,7 +24,7 @@ import { resolveFuncTupleType } from "./resolveFuncTupleType";
 import { ops } from "./ops";
 import { freshIdentifier } from "./freshIdentifier";
 import { idTextErr, throwInternalCompilerError } from "../../errors";
-import { prettyPrint, prettyPrintAsmShuffle } from "../../prettyPrinter";
+import { prettyPrintAsmShuffle } from "../../prettyPrinter";
 
 export function writeCastedExpression(
     expression: AstExpression,
@@ -554,9 +554,7 @@ export function writeFunction(f: FunctionDescription, ctx: WriterContext) {
                 };
                 ctx.asm(
                     prettyPrintAsmShuffle(asmShuffleEscaped),
-                    fAst.instructions
-                        .map((instruction) => prettyPrint(instruction))
-                        .join(" "),
+                    fAst.instructions.join(" "),
                 );
             });
             if (f.isMutating) {
diff --git a/src/grammar/__snapshots__/grammar.spec.ts.snap b/src/grammar/__snapshots__/grammar.spec.ts.snap
index 161c90950..75a91ea99 100644
--- a/src/grammar/__snapshots__/grammar.spec.ts.snap
+++ b/src/grammar/__snapshots__/grammar.spec.ts.snap
@@ -576,17 +576,6 @@ Line 2, col 23:
 `;
 
 exports[`grammar should fail items-asm-fun-1 1`] = `
-"<unknown>:2:5: Parse error: expected "0X", "0x", "0", "1".."9", "_", "A".."Z", or "a".."z"
-
-Line 2, col 5:
-  1 | asm fun keccak256(s: Slice): Int {
-> 2 |     +
-          ^
-  3 |     INT
-"
-`;
-
-exports[`grammar should fail items-asm-fun-2 1`] = `
 "<unknown>:1:5: Parse error: expected ")"
 
 Line 1, col 5:
@@ -596,7 +585,7 @@ Line 1, col 5:
 "
 `;
 
-exports[`grammar should fail items-asm-fun-3 1`] = `
+exports[`grammar should fail items-asm-fun-2 1`] = `
 "<unknown>:1:9: Parse error: expected ")", "->", "_", "A".."Z", or "a".."z"
 
 Line 1, col 9:
@@ -606,7 +595,7 @@ Line 1, col 9:
 "
 `;
 
-exports[`grammar should fail items-asm-fun-4 1`] = `
+exports[`grammar should fail items-asm-fun-3 1`] = `
 "<unknown>:1:14: Parse error: expected "0" or "1".."9"
 
 Line 1, col 14:
@@ -616,7 +605,7 @@ Line 1, col 14:
 "
 `;
 
-exports[`grammar should fail items-asm-fun-5 1`] = `
+exports[`grammar should fail items-asm-fun-4 1`] = `
 "<unknown>:1:7: Parse error: expected "0" or "1".."9"
 
 Line 1, col 7:
@@ -3295,31 +3284,16 @@ exports[`grammar should parse expr-with-var 1`] = `
 
 exports[`grammar should parse items-asm-funs 1`] = `
 {
-  "id": 44,
+  "id": 46,
   "imports": [],
   "items": [
     {
       "attributes": [],
-      "id": 9,
+      "id": 6,
       "instructions": [
-        {
-          "id": 6,
-          "kind": "number",
-          "loc": 1,
-          "value": 1n,
-        },
-        {
-          "id": 7,
-          "kind": "id",
-          "loc": INT,
-          "text": "INT",
-        },
-        {
-          "id": 8,
-          "kind": "id",
-          "loc": HASHEXT_KECCAK256,
-          "text": "HASHEXT_KECCAK256",
-        },
+        "1",
+        "INT",
+        "HASHEXT_KECCAK256",
       ],
       "kind": "asm_function_def",
       "loc": asm fun keccak256(s: Slice): Int {
@@ -3370,38 +3344,33 @@ exports[`grammar should parse items-asm-funs 1`] = `
           "type": "extends",
         },
       ],
-      "id": 18,
+      "id": 14,
       "instructions": [
-        {
-          "id": 17,
-          "kind": "id",
-          "loc": LDVARUINT16,
-          "text": "LDVARUINT16",
-        },
+        "LDVARUINT16",
       ],
       "kind": "asm_function_def",
       "loc": asm( -> 1 0) extends fun loadCoins(self: Slice): Int {
     LDVARUINT16
 },
       "name": {
-        "id": 12,
+        "id": 9,
         "kind": "id",
         "loc": loadCoins,
         "text": "loadCoins",
       },
       "params": [
         {
-          "id": 16,
+          "id": 13,
           "kind": "typed_parameter",
           "loc": self: Slice,
           "name": {
-            "id": 14,
+            "id": 11,
             "kind": "id",
             "loc": self,
             "text": "self",
           },
           "type": {
-            "id": 15,
+            "id": 12,
             "kind": "type_id",
             "loc": Slice,
             "text": "Slice",
@@ -3409,7 +3378,7 @@ exports[`grammar should parse items-asm-funs 1`] = `
         },
       ],
       "return": {
-        "id": 13,
+        "id": 10,
         "kind": "type_id",
         "loc": Int,
         "text": "Int",
@@ -3418,13 +3387,13 @@ exports[`grammar should parse items-asm-funs 1`] = `
         "args": [],
         "ret": [
           {
-            "id": 10,
+            "id": 7,
             "kind": "number",
             "loc": 1,
             "value": 1n,
           },
           {
-            "id": 11,
+            "id": 8,
             "kind": "number",
             "loc": 0,
             "value": 0n,
@@ -3439,55 +3408,50 @@ exports[`grammar should parse items-asm-funs 1`] = `
           "type": "extends",
         },
       ],
-      "id": 29,
+      "id": 24,
       "instructions": [
-        {
-          "id": 28,
-          "kind": "id",
-          "loc": STDICT,
-          "text": "STDICT",
-        },
+        "STDICT",
       ],
       "kind": "asm_function_def",
       "loc": asm(c b) extends fun storeDict(b: Builder, c: Cell) {
     STDICT
 },
       "name": {
-        "id": 21,
+        "id": 17,
         "kind": "id",
         "loc": storeDict,
         "text": "storeDict",
       },
       "params": [
         {
-          "id": 24,
+          "id": 20,
           "kind": "typed_parameter",
           "loc": b: Builder,
           "name": {
-            "id": 22,
+            "id": 18,
             "kind": "id",
             "loc": b,
             "text": "b",
           },
           "type": {
-            "id": 23,
+            "id": 19,
             "kind": "type_id",
             "loc": Builder,
             "text": "Builder",
           },
         },
         {
-          "id": 27,
+          "id": 23,
           "kind": "typed_parameter",
           "loc": c: Cell,
           "name": {
-            "id": 25,
+            "id": 21,
             "kind": "id",
             "loc": c,
             "text": "c",
           },
           "type": {
-            "id": 26,
+            "id": 22,
             "kind": "type_id",
             "loc": Cell,
             "text": "Cell",
@@ -3498,13 +3462,13 @@ exports[`grammar should parse items-asm-funs 1`] = `
       "shuffle": {
         "args": [
           {
-            "id": 19,
+            "id": 15,
             "kind": "id",
             "loc": c,
             "text": "c",
           },
           {
-            "id": 20,
+            "id": 16,
             "kind": "id",
             "loc": b,
             "text": "b",
@@ -3520,55 +3484,50 @@ exports[`grammar should parse items-asm-funs 1`] = `
           "type": "extends",
         },
       ],
-      "id": 43,
+      "id": 37,
       "instructions": [
-        {
-          "id": 42,
-          "kind": "id",
-          "loc": LDIX,
-          "text": "LDIX",
-        },
+        "LDIX",
       ],
       "kind": "asm_function_def",
       "loc": asm(s len -> 1 0) extends fun loadInt(self: Slice, len: Int): Int {
     LDIX
 },
       "name": {
-        "id": 34,
+        "id": 29,
         "kind": "id",
         "loc": loadInt,
         "text": "loadInt",
       },
       "params": [
         {
-          "id": 38,
+          "id": 33,
           "kind": "typed_parameter",
           "loc": self: Slice,
           "name": {
-            "id": 36,
+            "id": 31,
             "kind": "id",
             "loc": self,
             "text": "self",
           },
           "type": {
-            "id": 37,
+            "id": 32,
             "kind": "type_id",
             "loc": Slice,
             "text": "Slice",
           },
         },
         {
-          "id": 41,
+          "id": 36,
           "kind": "typed_parameter",
           "loc": len: Int,
           "name": {
-            "id": 39,
+            "id": 34,
             "kind": "id",
             "loc": len,
             "text": "len",
           },
           "type": {
-            "id": 40,
+            "id": 35,
             "kind": "type_id",
             "loc": Int,
             "text": "Int",
@@ -3576,7 +3535,7 @@ exports[`grammar should parse items-asm-funs 1`] = `
         },
       ],
       "return": {
-        "id": 35,
+        "id": 30,
         "kind": "type_id",
         "loc": Int,
         "text": "Int",
@@ -3584,13 +3543,13 @@ exports[`grammar should parse items-asm-funs 1`] = `
       "shuffle": {
         "args": [
           {
-            "id": 30,
+            "id": 25,
             "kind": "id",
             "loc": s,
             "text": "s",
           },
           {
-            "id": 31,
+            "id": 26,
             "kind": "id",
             "loc": len,
             "text": "len",
@@ -3598,13 +3557,13 @@ exports[`grammar should parse items-asm-funs 1`] = `
         ],
         "ret": [
           {
-            "id": 32,
+            "id": 27,
             "kind": "number",
             "loc": 1,
             "value": 1n,
           },
           {
-            "id": 33,
+            "id": 28,
             "kind": "number",
             "loc": 0,
             "value": 0n,
@@ -3612,6 +3571,76 @@ exports[`grammar should parse items-asm-funs 1`] = `
         ],
       },
     },
+    {
+      "attributes": [],
+      "id": 43,
+      "instructions": [
+        "x{02}",
+        "SDBEGINSQ",
+      ],
+      "kind": "asm_function_def",
+      "loc": asm fun checkAndRemoveAddExtensionPrefix(self: Slice): Int {
+    x{02} SDBEGINSQ
+},
+      "name": {
+        "id": 38,
+        "kind": "id",
+        "loc": checkAndRemoveAddExtensionPrefix,
+        "text": "checkAndRemoveAddExtensionPrefix",
+      },
+      "params": [
+        {
+          "id": 42,
+          "kind": "typed_parameter",
+          "loc": self: Slice,
+          "name": {
+            "id": 40,
+            "kind": "id",
+            "loc": self,
+            "text": "self",
+          },
+          "type": {
+            "id": 41,
+            "kind": "type_id",
+            "loc": Slice,
+            "text": "Slice",
+          },
+        },
+      ],
+      "return": {
+        "id": 39,
+        "kind": "type_id",
+        "loc": Int,
+        "text": "Int",
+      },
+      "shuffle": {
+        "args": [],
+        "ret": [],
+      },
+    },
+    {
+      "attributes": [],
+      "id": 45,
+      "instructions": [
+        "-ROT",
+      ],
+      "kind": "asm_function_def",
+      "loc": asm fun checkAndRemoveAddExtensionPrefix() {
+    -ROT
+},
+      "name": {
+        "id": 44,
+        "kind": "id",
+        "loc": checkAndRemoveAddExtensionPrefix,
+        "text": "checkAndRemoveAddExtensionPrefix",
+      },
+      "params": [],
+      "return": null,
+      "shuffle": {
+        "args": [],
+        "ret": [],
+      },
+    },
   ],
   "kind": "module",
 }
diff --git a/src/grammar/ast.ts b/src/grammar/ast.ts
index 90a022d57..44a83a0ea 100644
--- a/src/grammar/ast.ts
+++ b/src/grammar/ast.ts
@@ -62,7 +62,7 @@ export type AstAsmFunctionDef = {
     loc: SrcInfo;
 };
 
-export type AstAsmInstruction = AstId | AstNumber;
+export type AstAsmInstruction = string;
 export type AstAsmShuffle = {
     args: AstId[];
     ret: AstNumber[];
@@ -661,7 +661,6 @@ export type AstNode =
     | AstFuncId
     | AstExpression
     | AstStatement
-    | AstAsmInstruction
     | AstTypeDecl
     | AstFieldDecl
     | AstTypedParameter
diff --git a/src/grammar/compare.ts b/src/grammar/compare.ts
index eb9307396..eb5ab0251 100644
--- a/src/grammar/compare.ts
+++ b/src/grammar/compare.ts
@@ -51,6 +51,7 @@ import {
     AstNode,
     AstFuncId,
     AstAsmFunctionDef,
+    AstAsmInstruction,
 } from "./ast";
 import { AstRenamer } from "./rename";
 import { throwInternalCompilerError } from "../errors";
@@ -159,7 +160,7 @@ export class AstComparator {
                     this.compare(funcName1, funcName2) &&
                     this.compareNullableNodes(returnType1, returnType2) &&
                     this.compareArray(params1, params2) &&
-                    this.compareArray(instructions1, instructions2)
+                    this.compareAsmInstructions(instructions1, instructions2)
                 );
             }
             case "function_decl": {
@@ -788,6 +789,16 @@ export class AstComparator {
         return this.compareArray(nodes1, nodes2);
     }
 
+    private compareAsmInstructions(
+        instructions1: AstAsmInstruction[],
+        instructions2: AstAsmInstruction[],
+    ): boolean {
+        if (instructions1.length !== instructions2.length) {
+            return false;
+        }
+        return instructions1.every((val1, i1) => val1 === instructions2[i1]);
+    }
+
     private compareAttributes<
         T extends
             | AstFunctionAttribute
diff --git a/src/grammar/grammar.ohm b/src/grammar/grammar.ohm
index 20726167b..e2c821e05 100644
--- a/src/grammar/grammar.ohm
+++ b/src/grammar/grammar.ohm
@@ -22,7 +22,7 @@ Tact {
     ModuleFunction = FunctionDefinition
                    | AsmFunction
 
-    AsmFunction = "asm" AsmShuffle? FunctionAttribute* fun id Parameters (":" Type)? "{" AsmInstruction+ "}"
+    AsmFunction = "asm" AsmShuffle? FunctionAttribute* fun id Parameters (":" Type)? "{" asmInstruction+ "}"
 
     ModuleConstant = ConstantDefinition
 
@@ -98,9 +98,8 @@ Tact {
              | external "(" Parameter? ")" "{" Statement* "}" --externalRegular
              | external "(" stringLiteral ")" "{" Statement* "}" --externalComment
 
-    AsmInstruction = id
-                   | integerLiteralDec
-                   | integerLiteralHex
+    asmInstruction = ("x" | "X" | "b" | "B") "{" hexDigit* "}" --data
+                   | ~comment (~space ~"}" any)+ --any
 
     Statement = StatementLet
               | StatementBlock
diff --git a/src/grammar/grammar.ts b/src/grammar/grammar.ts
index ef589b4ad..63db0fea0 100644
--- a/src/grammar/grammar.ts
+++ b/src/grammar/grammar.ts
@@ -361,9 +361,7 @@ semantics.addOperation<AstNode>("astOfItem", {
             name: funId.astOfExpression(),
             return: unwrapOptNode(optReturnType, (t) => t.astOfType()),
             params: funParameters.astsOfList(),
-            instructions: asmInstructions.children.map((s) =>
-                s.astOfExpression(),
-            ),
+            instructions: asmInstructions.children.map((s) => s.sourceString),
             loc: createRef(this),
         });
     },
diff --git a/src/grammar/hash.ts b/src/grammar/hash.ts
index ab2bf996d..f4ec27fc2 100644
--- a/src/grammar/hash.ts
+++ b/src/grammar/hash.ts
@@ -24,7 +24,6 @@ import {
     AstNode,
     AstAsmFunctionDef,
     AstAsmInstruction,
-    idText,
 } from "./ast";
 import { createHash } from "crypto";
 import { throwInternalCompilerError } from "../errors";
@@ -305,16 +304,7 @@ export class AstHasher {
     }
 
     private hashInstructions(instructions: AstAsmInstruction[]): string {
-        return instructions
-            .map((instruction) => {
-                switch (instruction.kind) {
-                    case "number":
-                        return instruction.value.toString();
-                    case "id":
-                        return idText(instruction);
-                }
-            })
-            .join("|");
+        return instructions.join("|");
     }
 
     private hashStructFieldInitializer(
diff --git a/src/grammar/iterators.ts b/src/grammar/iterators.ts
index f4fc22d74..4a8501470 100644
--- a/src/grammar/iterators.ts
+++ b/src/grammar/iterators.ts
@@ -46,9 +46,6 @@ export function traverse(node: AstNode, callback: (node: AstNode) => void) {
             node.params.forEach((e) => {
                 traverse(e, callback);
             });
-            node.instructions.forEach((e) => {
-                traverse(e, callback);
-            });
             break;
         case "function_decl":
             traverse(node.name, callback);
diff --git a/src/grammar/test-failed/items-asm-fun-1.tact b/src/grammar/test-failed/items-asm-fun-1.tact
index 8e7466355..bc4e3061e 100644
--- a/src/grammar/test-failed/items-asm-fun-1.tact
+++ b/src/grammar/test-failed/items-asm-fun-1.tact
@@ -1,6 +1,4 @@
-asm fun keccak256(s: Slice): Int {
-    +
-    INT
-    HASHEXT_KECCAK256
+asm(1 0) extends fun loadCoins(self: Slice): Int {
+    LDVARUINT16
 }
 
diff --git a/src/grammar/test-failed/items-asm-fun-2.tact b/src/grammar/test-failed/items-asm-fun-2.tact
index bc4e3061e..8df0bd748 100644
--- a/src/grammar/test-failed/items-asm-fun-2.tact
+++ b/src/grammar/test-failed/items-asm-fun-2.tact
@@ -1,4 +1,4 @@
-asm(1 0) extends fun loadCoins(self: Slice): Int {
-    LDVARUINT16
+asm(c b 42) extends fun storeDict(b: Builder, c: Cell) {
+    STDICT
 }
 
diff --git a/src/grammar/test-failed/items-asm-fun-3.tact b/src/grammar/test-failed/items-asm-fun-3.tact
index 8df0bd748..f1eb4c247 100644
--- a/src/grammar/test-failed/items-asm-fun-3.tact
+++ b/src/grammar/test-failed/items-asm-fun-3.tact
@@ -1,4 +1,4 @@
-asm(c b 42) extends fun storeDict(b: Builder, c: Cell) {
-    STDICT
+asm(s len -> len 1 0) extends fun loadInt(self: Slice, len: Int): Int {
+    LDIX
 }
 
diff --git a/src/grammar/test-failed/items-asm-fun-4.tact b/src/grammar/test-failed/items-asm-fun-4.tact
index f1eb4c247..46713e863 100644
--- a/src/grammar/test-failed/items-asm-fun-4.tact
+++ b/src/grammar/test-failed/items-asm-fun-4.tact
@@ -1,4 +1,3 @@
-asm(s len -> len 1 0) extends fun loadInt(self: Slice, len: Int): Int {
+asm(->) extends fun loadInt(self: Slice, len: Int): Int {
     LDIX
 }
-
diff --git a/src/grammar/test-failed/items-asm-fun-5.tact b/src/grammar/test-failed/items-asm-fun-5.tact
deleted file mode 100644
index 46713e863..000000000
--- a/src/grammar/test-failed/items-asm-fun-5.tact
+++ /dev/null
@@ -1,3 +0,0 @@
-asm(->) extends fun loadInt(self: Slice, len: Int): Int {
-    LDIX
-}
diff --git a/src/grammar/test/items-asm-funs.tact b/src/grammar/test/items-asm-funs.tact
index 7abb7ac57..7525e63d1 100644
--- a/src/grammar/test/items-asm-funs.tact
+++ b/src/grammar/test/items-asm-funs.tact
@@ -15,3 +15,11 @@ asm(c b) extends fun storeDict(b: Builder, c: Cell) {
 asm(s len -> 1 0) extends fun loadInt(self: Slice, len: Int): Int {
     LDIX
 }
+
+asm fun checkAndRemoveAddExtensionPrefix(self: Slice): Int {
+    x{02} SDBEGINSQ
+}
+
+asm fun checkAndRemoveAddExtensionPrefix() {
+    -ROT
+}
diff --git a/src/prettyPrinter.ts b/src/prettyPrinter.ts
index b8277aeab..5b3d10a21 100644
--- a/src/prettyPrinter.ts
+++ b/src/prettyPrinter.ts
@@ -589,12 +589,7 @@ export class PrettyPrinter {
     }
 
     ppAstAsmInstruction(instruction: AstAsmInstruction): string {
-        switch (instruction.kind) {
-            case "number":
-                return `${this.indent()}${instruction.value.toString()}`;
-            case "id":
-                return `${this.indent()}${idText(instruction)}`;
-        }
+        return `${this.indent()}${instruction}`;
     }
 
     ppAstStatementLet(statement: AstStatementLet): string {
diff --git a/src/types/__snapshots__/resolveDescriptors.spec.ts.snap b/src/types/__snapshots__/resolveDescriptors.spec.ts.snap
index 5135364ab..a8080b3fe 100644
--- a/src/types/__snapshots__/resolveDescriptors.spec.ts.snap
+++ b/src/types/__snapshots__/resolveDescriptors.spec.ts.snap
@@ -636,14 +636,9 @@ exports[`resolveDescriptors should resolve descriptors for asm-extends-fun 1`] =
               "type": "mutates",
             },
           ],
-          "id": 13,
+          "id": 12,
           "instructions": [
-            {
-              "id": 12,
-              "kind": "id",
-              "loc": LDREF,
-              "text": "LDREF",
-            },
+            "LDREF",
           ],
           "kind": "asm_function_def",
           "loc": asm(-> 1 0) extends mutates fun loadRef(self: Slice): Cell { LDREF },
@@ -799,14 +794,9 @@ exports[`resolveDescriptors should resolve descriptors for asm-fun-no-arg-shuffl
   {
     "ast": {
       "attributes": [],
-      "id": 10,
+      "id": 9,
       "instructions": [
-        {
-          "id": 9,
-          "kind": "id",
-          "loc": NOP,
-          "text": "NOP",
-        },
+        "NOP",
       ],
       "kind": "asm_function_def",
       "loc": asm(-> 0) fun foo(x: Int): Int {
@@ -928,20 +918,10 @@ exports[`resolveDescriptors should resolve descriptors for asm-fun-no-ret-shuffl
   {
     "ast": {
       "attributes": [],
-      "id": 14,
+      "id": 12,
       "instructions": [
-        {
-          "id": 12,
-          "kind": "id",
-          "loc": DROP,
-          "text": "DROP",
-        },
-        {
-          "id": 13,
-          "kind": "id",
-          "loc": DROP,
-          "text": "DROP",
-        },
+        "DROP",
+        "DROP",
       ],
       "kind": "asm_function_def",
       "loc": asm(y x) fun foo(x: Int, y: Int) {
@@ -1094,14 +1074,9 @@ exports[`resolveDescriptors should resolve descriptors for asm-fun-no-shuffle 2`
   {
     "ast": {
       "attributes": [],
-      "id": 8,
+      "id": 7,
       "instructions": [
-        {
-          "id": 7,
-          "kind": "id",
-          "loc": DROP,
-          "text": "DROP",
-        },
+        "DROP",
       ],
       "kind": "asm_function_def",
       "loc": asm fun foo(x: Int) {
@@ -1359,14 +1334,9 @@ exports[`resolveDescriptors should resolve descriptors for asm-fun-shuffle-pair
   {
     "ast": {
       "attributes": [],
-      "id": 22,
+      "id": 21,
       "instructions": [
-        {
-          "id": 21,
-          "kind": "id",
-          "loc": SWAP,
-          "text": "SWAP",
-        },
+        "SWAP",
       ],
       "kind": "asm_function_def",
       "loc": asm(-> 1 0) fun foo(x: Int, y: Int): Pair {