diff --git a/src/fcstr.c b/src/fcstr.c
index 2f2cd4d..3b84ac0 100644
--- a/src/fcstr.c
+++ b/src/fcstr.c
@@ -733,7 +733,10 @@ FcStrBufDone (FcStrBuf *buf)
 {
     FcChar8 *ret;
 
-    ret = malloc (buf->len + 1);
+    if (buf->failed)
+	ret = NULL;
+    else
+	ret = malloc (buf->len + 1);
     if (ret)
     {
 	FcMemAlloc (FC_MEM_STRING, buf->len + 1);
@@ -752,6 +755,9 @@ FcStrBufChar (FcStrBuf *buf, FcChar8 c)
 	FcChar8	    *new;
 	int	    size;
 
+	if (buf->failed)
+	    return FcFalse;
+
 	if (buf->allocated)
 	{
 	    size = buf->size * 2;