diff --git a/lib/isc/include/isc/platform.h.in b/lib/isc/include/isc/platform.h.in
index 662986d004..77c7af944a 100644
--- a/lib/isc/include/isc/platform.h.in
+++ b/lib/isc/include/isc/platform.h.in
@@ -58,6 +58,11 @@
  */
 @ISC_PLATFORM_NEEDPORTT@
 
+/*
+ * If the system needs strsep(), ISC_PLATFORM_NEEDSTRSEP will be defined.
+ */
+@ISC_PLATFORM_NEEDSTRSEP@
+
 /*
  * Define either ISC_PLATFORM_BSD44MSGHDR or ISC_PLATFORM_BSD43MSGHDR
  */