diff --git a/lib/c.c b/lib/c.c
index 98a6d27d..1211065b 100644
--- a/lib/c.c
+++ b/lib/c.c
@@ -2,16 +2,15 @@
 
 #define NULL 0
 
-#ifdef __arm__
+#if defined(__arm__)
 #define __syscall_exit 1
 #define __syscall_read 3
 #define __syscall_write 4
 #define __syscall_close 6
 #define __syscall_open 5
 #define __syscall_brk 45
-#endif
 
-#ifdef __riscv
+#elif defined(__riscv)
 #define __syscall_exit 93
 #define __syscall_read 63
 #define __syscall_write 64
@@ -19,6 +18,7 @@
 #define __syscall_open 1024
 #define __syscall_openat 56
 #define __syscall_brk 214
+
 #endif
 
 typedef int FILE;
@@ -326,19 +326,17 @@ void abort()
 FILE *fopen(char *filename, char *mode)
 {
     if (!strcmp(mode, "wb"))
-#ifdef __arm__
+#if defined(__arm__)
         return __syscall(__syscall_open, filename, 65, 0x1fd);
-#endif
-/* FIXME: mode not work currently in RISC-V */
-#ifdef __riscv
-    return __syscall(__syscall_openat, -100, filename, 65, 0x1fd);
+#elif defined(__riscv)
+        /* FIXME: mode not work currently in RISC-V */
+        return __syscall(__syscall_openat, -100, filename, 65, 0x1fd);
 #endif
     if (!strcmp(mode, "rb"))
-#ifdef __arm__
+#if defined(__arm__)
         return __syscall(__syscall_open, filename, 0, 0);
-#endif
-#ifdef __riscv
-    return __syscall(__syscall_openat, -100, filename, 0, 0);
+#elif defined(__riscv)
+        return __syscall(__syscall_openat, -100, filename, 0, 0);
 #endif
 
     abort();
diff --git a/src/cfront.c b/src/cfront.c
index 2cd8dfc4..e5a10ff4 100644
--- a/src/cfront.c
+++ b/src/cfront.c
@@ -112,6 +112,8 @@ char token_str[MAX_TOKEN_LEN];
 token_t next_token;
 char next_char;
 
+int preproc_match;
+
 void skip_whitespace()
 {
     while (is_whitespace(next_char))
@@ -126,6 +128,28 @@ char read_char(int is_skip_space)
     return next_char;
 }
 
+/*
+ * get alias name from defined() directive
+ * i.e., get __arm__ from defined(__arm__)
+ */
+void read_alias_name_from_defined(char *alias_name, char *src)
+{
+    int i;
+
+    src = src + 8; /* skip defined( */
+    i = 0;
+    while (src[i] != ')') {
+        alias_name[i] = src[i];
+        i++;
+    }
+    alias_name[i] = 0;
+}
+
+char peek_char(int offset)
+{
+    return SOURCE[source_idx + offset];
+}
+
 token_t get_next_token()
 {
     token_str[0] = 0;
@@ -133,6 +157,10 @@ token_t get_next_token()
     /* partial preprocessor */
     if (next_char == '#') {
         int i = 0;
+        char *alias = NULL;
+        char alias_name[MAX_TOKEN_LEN];
+        char peek_c;
+
         do {
             token_str[i++] = next_char;
         } while (is_alnum(read_char(0)));
@@ -150,8 +178,84 @@ token_t get_next_token()
             skip_whitespace();
             return T_define;
         }
+        if (!strcmp(token_str, "#if")) {
+            preproc_match = 0;
+            i = 0;
+            do {
+                token_str[i++] = next_char;
+            } while (read_char(0) != '\n');
+            token_str[i] = 0;
+
+            if (!strncmp(token_str, "defined", 7)) {
+                read_alias_name_from_defined(alias_name, token_str);
+                alias = find_alias(alias_name);
+                if (alias) {
+                    preproc_match = 1;
+                    skip_whitespace();
+                    return get_next_token();
+                }
+                /* skip lines until #elif or #else or #endif */
+                do {
+                    skip_whitespace();
+                    i = 0;
+                    do {
+                        token_str[i++] = next_char;
+                    } while (read_char(0) != '\n');
+                    token_str[i] = 0;
+                    read_char(1);
+                    peek_c = peek_char(1);
+                } while (next_char != '#' ||
+                         (next_char == '#' && peek_c == 'd'));
+                skip_whitespace();
+                return get_next_token();
+            }
+        }
+        if (!strcmp(token_str, "#elif")) {
+            if (preproc_match) {
+                do {
+                    skip_whitespace();
+                    i = 0;
+                    do {
+                        token_str[i++] = next_char;
+                    } while (read_char(0) != '\n');
+                    token_str[i] = 0;
+                } while (strcmp(token_str, "#endif"));
+                skip_whitespace();
+                return get_next_token();
+            }
+
+            i = 0;
+            do {
+                token_str[i++] = next_char;
+            } while (read_char(0) != '\n');
+            token_str[i] = 0;
+
+            if (!strncmp(token_str, "defined", 7)) {
+                read_alias_name_from_defined(alias_name, token_str);
+                alias = find_alias(alias_name);
+                if (alias) {
+                    preproc_match = 1;
+                    skip_whitespace();
+                    return get_next_token();
+                }
+                /* skip lines until #elif or #else or #endif */
+                do {
+                    skip_whitespace();
+                    i = 0;
+                    do {
+                        token_str[i++] = next_char;
+                    } while (read_char(0) != '\n');
+                    token_str[i] = 0;
+                    read_char(1);
+                    peek_c = peek_char(1);
+                } while (next_char != '#' ||
+                         (next_char == '#' && peek_c == 'd'));
+                skip_whitespace();
+                return get_next_token();
+            }
+        }
         if (!strcmp(token_str, "#ifdef")) {
-            char *alias = NULL;
+            preproc_match = 0;
             i = 0;
             do {
                 token_str[i++] = next_char;
@@ -161,6 +265,7 @@ token_t get_next_token()
             alias = find_alias(token_str);
             if (alias) {
                 /* ignore #else directive */
+                preproc_match = 1;
                 skip_whitespace();
                 return get_next_token();
             }
@@ -177,8 +282,17 @@ token_t get_next_token()
             return get_next_token();
         }
         if (!strcmp(token_str, "#else")) {
-            /* reach here means previous alias is defined so skip lines until
-             * #endif */
+            /*
+             * reach here has 2 possible cases:
+             * 1. reach #ifdef preprocessor directive
+             * 2. conditional expression in #elif is false
+             */
+
+            if (!preproc_match) {
+                skip_whitespace();
+                return get_next_token();
+            }
+            /* skip lines until #else or #endif */
             do {
                 skip_whitespace();
                 i = 0;
@@ -191,6 +305,7 @@ token_t get_next_token()
             return get_next_token();
         }
         if (!strcmp(token_str, "#endif")) {
+            preproc_match = 0;
             skip_whitespace();
             return get_next_token();
         }
diff --git a/tests/driver.sh b/tests/driver.sh
index 61c26fb8..49e057f4 100755
--- a/tests/driver.sh
+++ b/tests/driver.sh
@@ -339,4 +339,22 @@ int main()
 }
 EOF
 
+# #if defined(...) ... #elif defined(...) ... #else ... #endif
+try_ 0 << EOF
+#define A 0
+#define B 0xDEAD
+int main()
+{
+    int x;
+#if defined(A)
+    x = A;
+#elif defined(B)
+    x = B;
+#else
+    x = 0xCAFE
+#endif
+    return x;
+}
+EOF
+
 echo OK