1 files changed, 12 insertions, 4 deletions

diff --git a/string.c b/string.c
index 61b0a96ef6..d2737045e1 100644
--- a/string.c
+++ b/string.c
@@ -1328,12 +1328,20 @@ rb_str_modify_expand(VALUE str, long expand)
     if (expand < 0) {
 	rb_raise(rb_eArgError, "negative expanding string size");
     }
-    if (!str_independent(str) ||
-	(expand > 0 &&
-	 (!STR_EMBED_P(str) ||
-	  RSTRING_LEN(str) + expand > RSTRING_EMBED_LEN_MAX))) {
+    if (!str_independent(str)) {
 	str_make_independent_expand(str, expand);
     }
+    else if (expand > 0) {
+	long len = RSTRING_LEN(str);
+	long capa = len + expand;
+	if (!STR_EMBED_P(str)) {
+	    REALLOC_N(RSTRING(str)->as.heap.ptr, char, capa+1);
+	    RSTRING(str)->as.heap.aux.capa = capa;
+	}
+	else if (capa > RSTRING_EMBED_LEN_MAX) {
+	    str_make_independent_expand(str, expand);
+	}
+    }
     ENC_CODERANGE_CLEAR(str);
 }