diff --git a/src/cycleclock.h b/src/cycleclock.h
index 31108046..e4825d4b 100644
--- a/src/cycleclock.h
+++ b/src/cycleclock.h
@@ -113,11 +113,11 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
   uint32_t pmuseren;
   uint32_t pmcntenset;
   // Read the user mode perf monitor counter access permissions.
-  asm("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
+  asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
   if (pmuseren & 1) {  // Allows reading perfmon counters for user mode code.
-    asm("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
+    asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
     if (pmcntenset & 0x80000000ul) {  // Is it counting?
-      asm("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
+      asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
       // The counter is set up to count every 64th cycle
       return static_cast<int64_t>(pmccntr) * 64;  // Should optimize to << 6
     }