diff --git a/src/util/arch/arm/simd_utils.h b/src/util/arch/arm/simd_utils.h
index 764d26fd..902d3624 100644
--- a/src/util/arch/arm/simd_utils.h
+++ b/src/util/arch/arm/simd_utils.h
@@ -420,8 +420,9 @@ m128 load_m128_from_u64a(const u64a *p) {
 
 static really_inline u32 extract32from128(const m128 in, unsigned imm) {
 #if defined(HAVE__BUILTIN_CONSTANT_P)
-    if (__builtin_constant_p(b)) {
+    if (__builtin_constant_p(imm)) {
         return vgetq_lane_u32((uint32x4_t) in, imm);
+    }
 #endif
     switch (imm) {
     case 0:
@@ -444,8 +445,9 @@ static really_inline u32 extract32from128(const m128 in, unsigned imm) {
 
 static really_inline u64a extract64from128(const m128 in, unsigned imm) {
 #if defined(HAVE__BUILTIN_CONSTANT_P)
-    if (__builtin_constant_p(b)) {
+    if (__builtin_constant_p(imm)) {
         return vgetq_lane_u64((uint64x2_t) in, imm);
+    }
 #endif
     switch (imm) {
     case 0: