diff --git a/options/m_property.c b/options/m_property.c
index d16767b34d..f4810579da 100644
--- a/options/m_property.c
+++ b/options/m_property.c
@@ -273,7 +273,8 @@ static int m_property_do_bstr(const struct m_property *prop_list, bstr name,
 static void append_str(char **s, int *len, bstr append)
 {
     MP_TARRAY_GROW(NULL, *s, *len + append.len);
-    memcpy(*s + *len, append.start, append.len);
+    if (append.len)
+        memcpy(*s + *len, append.start, append.len);
     *len = *len + append.len;
 }