diff --git a/std/internal/math/biguintcore.d b/std/internal/math/biguintcore.d
index c8c192986..6d91114ba 100644
--- a/std/internal/math/biguintcore.d
+++ b/std/internal/math/biguintcore.d
@@ -79,8 +79,7 @@ public:
 struct BigUint {
 private:
     invariant() {
-    // @@@BUG@@@ Compiler bug 3986:
-        //assert( data.length == 1 || data[$-1] != 0 );
+        assert( data.length == 1 || data[$-1] != 0 );
     }
     BigDigit [] data = ZERO; 
     this(BigDigit [] x) {