diff --git a/lib/isc/include/isc/overflow.h b/lib/isc/include/isc/overflow.h
index c272cfa879..225161934e 100644
--- a/lib/isc/include/isc/overflow.h
+++ b/lib/isc/include/isc/overflow.h
@@ -37,7 +37,7 @@
  *	INSIST(!overflow);
  */
 
-#if HAVE_BUILTIN_MUL_OVERFLOW
+#ifdef HAVE_BUILTIN_MUL_OVERFLOW
 #define ISC_OVERFLOW_MUL(a, b, cp) __builtin_mul_overflow(a, b, cp)
 #else
 #define ISC_OVERFLOW_MUL(a, b, cp)                                           \
@@ -45,7 +45,7 @@
 						: true)
 #endif
 
-#if HAVE_BUILTIN_ADD_OVERFLOW
+#ifdef HAVE_BUILTIN_ADD_OVERFLOW
 #define ISC_OVERFLOW_ADD(a, b, cp) __builtin_add_overflow(a, b, cp)
 #else
 #define ISC_OVERFLOW_ADD(a, b, cp)                                           \
@@ -53,7 +53,7 @@
 						: true)
 #endif
 
-#if HAVE_BUILTIN_SUB_OVERFLOW
+#ifdef HAVE_BUILTIN_SUB_OVERFLOW
 #define ISC_OVERFLOW_SUB(a, b, cp) __builtin_sub_overflow(a, b, cp)
 #else
 #define ISC_OVERFLOW_SUB(a, b, cp)                                           \