diff --git a/icu4c/source/tools/genrb/reslist.c b/icu4c/source/tools/genrb/reslist.c
index 3f0bdac460a..f95d5111931 100644
--- a/icu4c/source/tools/genrb/reslist.c
+++ b/icu4c/source/tools/genrb/reslist.c
@@ -461,7 +461,7 @@ struct SResource *string_open(struct SRBRoot *bundle, char *tag, UChar *value, i
     }
 
     uprv_memcpy(res->u.fString.fChars, value, sizeof(UChar) * (len + 1));
-    res->fSize = sizeof(int32_t) + sizeof(UChar) * (len);
+    res->fSize = sizeof(int32_t) + sizeof(UChar) * (len+1);
 
     return res;
 }