diff --git a/libavformat/nistspheredec.c b/libavformat/nistspheredec.c
index 76f65ec6e0..2c96686342 100644
--- a/libavformat/nistspheredec.c
+++ b/libavformat/nistspheredec.c
@@ -36,7 +36,7 @@ static int nist_read_header(AVFormatContext *s)
 {
     char buffer[32], coding[32] = "pcm", format[32] = "01";
     int bps = 0, be = 0;
-    int32_t header_size;
+    int32_t header_size = -1;
     AVStream *st;
 
     st = avformat_new_stream(s, NULL);