diff --git a/libs/util/dstring.c b/libs/util/dstring.c
index d42430ad1..18e6358b6 100644
--- a/libs/util/dstring.c
+++ b/libs/util/dstring.c
@@ -296,8 +296,9 @@ _dvsprintf (dstring_t *dstr, int offs, const char *fmt, va_list args)
 	if (!dstr->truesize)
 		dstring_clearstr (dstr); // Make it a string
 	// Some vsnprintf implementations return -1 on truncation
-	while ((size = vsnprintf (dstr->str + offs, dstr->truesize - offs, fmt, args)) == -1) {
-		dstr->size = (dstr->truesize & 1023) + 1024;
+	while ((size = vsnprintf (dstr->str + offs, dstr->truesize - offs, fmt,
+							  args)) == -1) {
+		dstr->size = (dstr->truesize & ~1023) + 1024;
 		dstring_adjust (dstr);
 #ifdef VA_LIST_IS_ARRAY
 		VA_COPY (args, tmp_args);