diff --git a/xwords4/common/memstream.c b/xwords4/common/memstream.c
index 7b87eed52..37b7829e4 100644
--- a/xwords4/common/memstream.c
+++ b/xwords4/common/memstream.c
@@ -268,9 +268,13 @@ putOneBit( MemStreamCtxt* stream, XP_U16 bit )
 } /* putOneBit */
 
 static void
-mem_stream_putBits( XWStreamCtxt* p_sctx, XP_U16 nBits, XP_U32 data )
+mem_stream_putBits( XWStreamCtxt* p_sctx, XP_U16 nBits, XP_U32 data
+                    DBG_LINE_FILE_FORMAL )
 {
     MemStreamCtxt* stream = (MemStreamCtxt*)p_sctx;
+#ifdef DEBUG
+    XP_U16 origBits = nBits;
+#endif
 
     XP_ASSERT( nBits > 0 );
 
@@ -278,7 +282,13 @@ mem_stream_putBits( XWStreamCtxt* p_sctx, XP_U16 nBits, XP_U32 data )
         putOneBit( stream, (XP_U16)(((data & 1L) != 0)? 1:0) );
         data >>= 1;
     }
-    XP_ASSERT( data == 0 );	/* otherwise nBits was too small */
+    XP_ASSERT( data == 0 );     /* otherwise nBits was too small */
+#ifdef DEBUG
+    if ( data != 0 ) {
+        XP_LOGF( "%s: nBits was %d from line %d, %s", __FUNCTION__, 
+                 origBits, lin, fil );
+    }
+#endif
 } /* mem_stream_putBits */
 
 static void
diff --git a/xwords4/common/xwstream.h b/xwords4/common/xwstream.h
index 2c094b3d8..b44f6455b 100644
--- a/xwords4/common/xwstream.h
+++ b/xwords4/common/xwstream.h
@@ -31,6 +31,14 @@ typedef XP_U32 XWStreamPos;     /* low 3 bits are bit offset; rest byte offset *
 enum { POS_READ, POS_WRITE };
 typedef XP_U8 PosWhich;
 
+#ifdef DEBUG
+# define DBG_LINE_FILE_FORMAL  , XP_U16 lin, const char* fil
+# define DBG_LINE_FILE_PARM  , __LINE__, __FILE__
+#else
+# define DBG_LINE_FILE_FORMAL
+# define DBG_LINE_FILE_PARM
+#endif
+
 typedef struct StreamCtxVTable {
     void (*m_stream_destroy)( XWStreamCtxt* dctx );
 
@@ -47,7 +55,8 @@ typedef struct StreamCtxVTable {
     void (*m_stream_putString)( XWStreamCtxt* dctx, const char* whence );
     void (*m_stream_putU16)( XWStreamCtxt* dctx, XP_U16 data );
     void (*m_stream_putU32)( XWStreamCtxt* dctx, XP_U32 data );
-    void (*m_stream_putBits)( XWStreamCtxt* dctx, XP_U16 nBits, XP_U32 bits );
+    void (*m_stream_putBits)( XWStreamCtxt* dctx, XP_U16 nBits, XP_U32 bits
+                              DBG_LINE_FILE_FORMAL );
 
     void (*m_stream_copyFromStream)( XWStreamCtxt* dctx, XWStreamCtxt* src,
                                      XP_U16 nBytes );
@@ -114,7 +123,7 @@ struct XWStreamCtxt {
          (sc)->vtable->m_stream_putU32((sc), (d))
 
 #define stream_putBits(sc, n, b) \
-         (sc)->vtable->m_stream_putBits((sc), (n), (b))
+         (sc)->vtable->m_stream_putBits((sc), (n), (b) DBG_LINE_FILE_PARM )
 
 #define stream_copyFromStream( sc, src, nb ) \
          (sc)->vtable->m_stream_copyFromStream((sc), (src), (nb))