diff --git a/arch/wasm32/atomic_arch.h b/arch/wasm32/atomic_arch.h
index d067050b..78b183cb 100644
--- a/arch/wasm32/atomic_arch.h
+++ b/arch/wasm32/atomic_arch.h
@@ -6,6 +6,13 @@
 
 #define a_barrier() syscall(__NR_membarrier)
 
-#define a_cas(p, t, s) (abort(), s)
+#define a_cas a_cas
+static inline int a_cas(volatile int *p, int t, int s)
+{
+  int old = *p;
+  if (old == t)
+    *p = s;
+  return old;
+}
 
 #define a_crash() abort()