diff --git a/string.c b/string.c
index 5f8bd363fc..ab04ac7596 100644
--- a/string.c
+++ b/string.c
@@ -5016,7 +5016,7 @@ rb_str_sub_bang(int argc, VALUE *argv, VALUE str)
 	if (rlen != plen) {
 	    memmove(p + beg0 + rlen, p + beg0 + plen, len - beg0 - plen);
 	}
-	memcpy(p + beg0, rp, rlen);
+	memmove(p + beg0, rp, rlen);
 	len += rlen - plen;
 	STR_SET_LEN(str, len);
 	TERM_FILL(&RSTRING_PTR(str)[len], TERM_LEN(str));
diff --git a/version.h b/version.h
index 62221f0ddf..e08522e1c5 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.5.6"
 #define RUBY_RELEASE_DATE "2019-08-27"
-#define RUBY_PATCHLEVEL 188
+#define RUBY_PATCHLEVEL 189
 
 #define RUBY_RELEASE_YEAR 2019
 #define RUBY_RELEASE_MONTH 8