diff --git a/compiler-rt/lib/builtins/arm/sync-ops.h b/compiler-rt/lib/builtins/arm/sync-ops.h
--- a/compiler-rt/lib/builtins/arm/sync-ops.h
+++ b/compiler-rt/lib/builtins/arm/sync-ops.h
@@ -19,14 +19,14 @@
   .thumb;                                                                      \
   .syntax unified;                                                             \
   DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_##op)                      \
-  dmb;                                                                         \
+  DMB;                                                                         \
   mov r12, r0;                                                                 \
   LOCAL_LABEL(tryatomic_##op) : ldrex r0, [r12];                               \
   op(r2, r0, r1);                                                              \
   strex r3, r2, [r12];                                                         \
   cmp r3, #0;                                                                  \
   bne LOCAL_LABEL(tryatomic_##op);                                             \
-  dmb;                                                                         \
+  DMB;                                                                         \
   bx lr
 
 #define SYNC_OP_8(op)                                                          \
@@ -35,14 +35,14 @@
   .syntax unified;                                                             \
   DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_##op)                      \
   push {r4, r5, r6, lr};                                                       \
-  dmb;                                                                         \
+  DMB;                                                                         \
   mov r12, r0;                                                                 \
   LOCAL_LABEL(tryatomic_##op) : ldrexd r0, r1, [r12];                          \
   op(r4, r5, r0, r1, r2, r3);                                                  \
   strexd r6, r4, r5, [r12];                                                    \
   cmp r6, #0;                                                                  \
   bne LOCAL_LABEL(tryatomic_##op);                                             \
-  dmb;                                                                         \
+  DMB;                                                                         \
   pop { r4, r5, r6, pc }
 
 #define MINMAX_4(rD, rN, rM, cmp_kind)                                         \
diff --git a/compiler-rt/lib/builtins/assembly.h b/compiler-rt/lib/builtins/assembly.h
--- a/compiler-rt/lib/builtins/assembly.h
+++ b/compiler-rt/lib/builtins/assembly.h
@@ -189,6 +189,14 @@
   JMP(ip)
 #endif
 
+#if __ARM_ARCH >= 7
+#define DMB dmb
+#elif __ARM_ARCH >= 6
+#define DMB mcr p15, #0, r0, c7, c10, #5
+#else
+#error only supported on ARMv6+
+#endif
+
 #if defined(USE_THUMB_2)
 #define WIDE(op) op.w
 #else