diff --git a/lang/b/lib/b.h b/lang/b/lib/b.h
index 1125452cd..36d9f38fd 100644
--- a/lang/b/lib/b.h
+++ b/lang/b/lib/b.h
@@ -14,6 +14,8 @@
 #error Unsupported EM_PSIZE
 #endif
 
+#define MASK ((1<<SHIFT)-1)
+
 extern FILE* input_unit;
 extern FILE* output_unit;
 
diff --git a/lang/b/lib/main.c b/lang/b/lib/main.c
index 44ea76c9b..1c3ce67a2 100644
--- a/lang/b/lib/main.c
+++ b/lang/b/lib/main.c
@@ -173,6 +173,8 @@ void patch_addresses(uintptr_t** p)
     while (*p)
     {
         uintptr_t* q = *p++;
+		if (*q & MASK)
+			abort();
         *q >>= SHIFT;
     }
 }