diff --git a/compiler/src/dmd/aggregate.d b/compiler/src/dmd/aggregate.d
index 78cb87f2fe7d..8970c351fc07 100644
--- a/compiler/src/dmd/aggregate.d
+++ b/compiler/src/dmd/aggregate.d
@@ -99,7 +99,7 @@ extern (C++) abstract class AggregateDeclaration : ScopeDsymbol
     StorageClass storage_class; ///
     uint structsize;            /// size of struct
     uint alignsize;             /// size of struct for alignment purposes
-    VarDeclarations fields;     /// VarDeclaration fields
+    VarDeclarations fields;     /// VarDeclaration fields including flattened AnonDeclaration members
     Dsymbol deferred;           /// any deferred semantic2() or semantic3() symbol
 
     /// specifies whether this is a D, C++, Objective-C or anonymous struct/class/interface
diff --git a/compiler/src/dmd/dstruct.d b/compiler/src/dmd/dstruct.d
index 64f19d932ebf..0ed194a17ef6 100644
--- a/compiler/src/dmd/dstruct.d
+++ b/compiler/src/dmd/dstruct.d
@@ -350,8 +350,18 @@ extern (C++) class StructDeclaration : AggregateDeclaration
 
         // Determine if struct is all zeros or not
         zeroInit = true;
+        auto lastOffset = -1;
         foreach (vd; fields)
         {
+            // First skip zero sized fields
+            if (vd.type.size(vd.loc) == 0)
+                continue;
+
+            // only consider first sized member of an (anonymous) union
+            if (vd.overlapped && vd.offset == lastOffset)
+                continue;
+            lastOffset = vd.offset;
+
             if (vd._init)
             {
                 if (vd._init.isVoidInitializer())
@@ -360,10 +370,6 @@ extern (C++) class StructDeclaration : AggregateDeclaration
                      */
                     continue;
 
-                // Zero size fields are zero initialized
-                if (vd.type.size(vd.loc) == 0)
-                    continue;
-
                 // Examine init to see if it is all 0s.
                 auto exp = vd.getConstInitializer();
                 if (!exp || !_isZeroInit(exp))
diff --git a/compiler/test/compilable/isZeroInit.d b/compiler/test/compilable/isZeroInit.d
index a64420febc0f..342dc07bf0f2 100644
--- a/compiler/test/compilable/isZeroInit.d
+++ b/compiler/test/compilable/isZeroInit.d
@@ -78,3 +78,45 @@ static if (is(Vector!(int[4])))
     static assert(__traits(isZeroInit, Holder!(Vector!(int[4]), 0)));
     static assert(!__traits(isZeroInit, Holder!(Vector!(int[4]), 1)));
 }
+
+// https://issues.dlang.org/show_bug.cgi?id=24776
+struct S6 {
+    union {
+        int i1;
+        float f1;
+    }
+}
+static assert(__traits(isZeroInit, S6));
+
+struct S7
+{
+    union {
+        float f2;
+        int i2;
+    }
+}
+static assert(!__traits(isZeroInit, S7));
+
+// https://issues.dlang.org/show_bug.cgi?id=23841
+union U
+{
+    float x = 0;
+    float y;
+}
+static assert(__traits(isZeroInit, U));
+
+union U2
+{
+    float x;
+    int y;
+}
+static assert(!__traits(isZeroInit, U2));
+
+struct S8 {
+    int[0] dummy; // same offset as anon union, but doesn't overlap; should be ignored anyway for zero-init check
+    union {
+        float f; // is the first member of the anon union and must be checked
+        int i;
+    }
+}
+static assert(!__traits(isZeroInit, S8));