diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index 85bbb9d1e7..6269e761ee 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -9283,7 +9283,7 @@ dns_zone_markdirty(dns_zone_t *zone) {
 			if (result != ISC_R_SUCCESS) {
 				UNLOCK_ZONE(zone);
 				secure = NULL;
-#if ISC_PLATFORM_USETHREADS
+#ifdef ISC_PLATFORM_USETHREADS
 				isc_thread_yield();
 #endif
 				goto again;
diff --git a/lib/isc/win32/include/isc/platform.h b/lib/isc/win32/include/isc/platform.h
index d632d3cf7e..ee4d536891 100644
--- a/lib/isc/win32/include/isc/platform.h
+++ b/lib/isc/win32/include/isc/platform.h
@@ -24,7 +24,7 @@
  ***** Platform-dependent defines.
  *****/
 
-#define ISC_PLATFORM_USETHREADS
+#define ISC_PLATFORM_USETHREADS 1
 
 /***
  *** Network.