diff --git a/icu4c/source/common/unicode/pwin32.h b/icu4c/source/common/unicode/pwin32.h
index 8626b8bc627..cd57a7d5ddb 100644
--- a/icu4c/source/common/unicode/pwin32.h
+++ b/icu4c/source/common/unicode/pwin32.h
@@ -39,7 +39,7 @@
  */
 
 #ifndef U_IOSTREAM_SOURCE
-#define U_IOSTREAM_SOURCE 199711
+#define U_IOSTREAM_SOURCE 198506
 #endif
 
 /* Determines whether specific types are available */