diff --git a/lib/isc/include/isc/mem.h b/lib/isc/include/isc/mem.h
index 28bdd64041..767f6d942f 100644
--- a/lib/isc/include/isc/mem.h
+++ b/lib/isc/include/isc/mem.h
@@ -186,7 +186,7 @@ extern unsigned int isc_mem_defaultflags;
  * see https://github.com/jemalloc/jemalloc/issues/2566
  * for more information.
  */
-#if HAVE_JEMALLOC
+#ifdef HAVE_JEMALLOC
 
 /*
  * cmocka.h has confliction definitions with the jemalloc header but we only
@@ -203,9 +203,9 @@ extern volatile void *isc__mem_malloc;
 		isc__mem_malloc = mallocx;                            \
 		ISC_INSIST(CMM_ACCESS_ONCE(isc__mem_malloc) != NULL); \
 	}
-#else
+#else /* HAVE_JEMALLOC */
 #define isc_mem_create(cp) isc__mem_create((cp)_ISC_MEM_FILELINE)
-#endif
+#endif /* HAVE_JEMALLOC */
 void
 isc__mem_create(isc_mem_t **_ISC_MEM_FLARG);
 
diff --git a/lib/isc/jemalloc_shim.h b/lib/isc/jemalloc_shim.h
index 1f6ef0fc44..056bfc1db8 100644
--- a/lib/isc/jemalloc_shim.h
+++ b/lib/isc/jemalloc_shim.h
@@ -13,7 +13,7 @@
 
 #pragma once
 
-#if !defined(HAVE_JEMALLOC)
+#ifndef HAVE_JEMALLOC
 
 #include <stddef.h>
 #include <string.h>
@@ -81,4 +81,4 @@ rallocx(void *ptr, size_t size, int flags) {
 	return ptr;
 }
 
-#endif /* !defined(HAVE_JEMALLOC) */
+#endif /* !HAVE_JEMALLOC */