diff --git a/src/cc65/declare.c b/src/cc65/declare.c
index 51490dd7d..06b1e314d 100644
--- a/src/cc65/declare.c
+++ b/src/cc65/declare.c
@@ -2137,6 +2137,7 @@ NextMember:
     ConsumeRCurly ();
 
     /* If we have data from a bit-field left, output it now */
+    CHECK(SI.ValBits < CHAR_BITS);
     OutputBitFieldData (&SI);
 
     /* If there are struct fields left, reserve additional storage */