diff --git a/src/core/bitmap.c b/src/core/bitmap.c
index 76fcef67..e9b6d904 100644
--- a/src/core/bitmap.c
+++ b/src/core/bitmap.c
@@ -76,7 +76,7 @@ int bitmap_test ( struct bitmap *bitmap, unsigned int bit ) {
 
 	if ( bit >= bitmap->length )
 		return 0;
-	return ( bitmap->blocks[index] & mask );
+	return ( ( bitmap->blocks[index] & mask ) != 0 );
 }
 
 /**
diff --git a/src/include/ipxe/bitmap.h b/src/include/ipxe/bitmap.h
index 38d1f221..b18584c1 100644
--- a/src/include/ipxe/bitmap.h
+++ b/src/include/ipxe/bitmap.h
@@ -33,7 +33,7 @@ typedef unsigned long bitmap_block_t;
  * @v bit		Bit index
  * @ret mask		Block mask
  */
-#define BITMAP_MASK( bit ) ( 1 << ( (bit) % BITMAP_BLKSIZE ) )
+#define BITMAP_MASK( bit ) ( 1UL << ( (bit) % BITMAP_BLKSIZE ) )
 
 /** A bitmap */
 struct bitmap {