diff --git a/library/constant_time.c b/library/constant_time.c
index 832ded9..cb5003d 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -78,7 +78,7 @@
      */
     uint32_t r;
 #if defined(MBEDTLS_CT_ARM_ASM)
-    asm volatile ("ldr %0, [%1]" : "=r" (r) : "r" (p) :);
+    __asm volatile ("ldr %0, [%1]" : "=r" (r) : "r" (p) :);
 #elif defined(MBEDTLS_CT_AARCH64_ASM)
     asm volatile ("ldr %w0, [%1]" : "=r" (r) : MBEDTLS_ASM_AARCH64_PTR_CONSTRAINT(p) :);
 #else