diff --git a/common_x86.h b/common_x86.h
index 8f1a0308d..4c17f3a04 100644
--- a/common_x86.h
+++ b/common_x86.h
@@ -356,4 +356,9 @@ REALNAME:
 
 #ifndef ALIGN_6
 #define ALIGN_6 .align 64
+
+// ffreep %st(0). 
+// Because Clang didn't support ffreep, we directly use the opcode.
+// Please check out http://www.sandpile.org/x86/opc_fpu.htm 
+#define ffreep .byte 0xdf, 0xc0 #
 #endif
diff --git a/common_x86_64.h b/common_x86_64.h
index 2dc788c93..e61e37e6b 100644
--- a/common_x86_64.h
+++ b/common_x86_64.h
@@ -448,4 +448,8 @@ REALNAME:
 #define ALIGN_6 .align 64
 #endif
 
+// ffreep %st(0). 
+// Because Clang didn't support ffreep, we directly use the opcode.
+// Please check out http://www.sandpile.org/x86/opc_fpu.htm 
+#define ffreep .byte 0xdf, 0xc0 #
 #endif