diff --git a/include/mbedtls/bn_mul.h b/include/mbedtls/bn_mul.h
index 7b8019c900..188d7f3bbb 100644
--- a/include/mbedtls/bn_mul.h
+++ b/include/mbedtls/bn_mul.h
@@ -42,6 +42,10 @@
 
 #if defined(MBEDTLS_HAVE_ASM)
 
+#ifndef asm
+#define asm __asm
+#endif
+
 #if defined(__GNUC__)
 #if defined(__i386__)
 
diff --git a/library/aesni.c b/library/aesni.c
index ff6c71dd3c..9982b3b102 100644
--- a/library/aesni.c
+++ b/library/aesni.c
@@ -37,6 +37,10 @@
 
 #include <string.h>
 
+#ifndef asm
+#define asm __asm
+#endif
+
 #if defined(MBEDTLS_HAVE_X86_64)
 
 /*
diff --git a/library/padlock.c b/library/padlock.c
index 3e9f9a9b53..e980d24df6 100644
--- a/library/padlock.c
+++ b/library/padlock.c
@@ -38,6 +38,10 @@
 
 #include <string.h>
 
+#ifndef asm
+#define asm __asm
+#endif
+
 #if defined(MBEDTLS_HAVE_X86)
 
 /*
diff --git a/library/timing.c b/library/timing.c
index 4ff11e79e1..bdbdccef1f 100644
--- a/library/timing.c
+++ b/library/timing.c
@@ -39,6 +39,10 @@
 
 #if !defined(MBEDTLS_TIMING_ALT)
 
+#ifndef asm
+#define asm __asm
+#endif
+
 #if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
 
 #include <windows.h>