diff --git a/src/aig/miniaig/minilut.h b/src/aig/miniaig/minilut.h
index fb5c6f06f..b080c983e 100644
--- a/src/aig/miniaig/minilut.h
+++ b/src/aig/miniaig/minilut.h
@@ -96,6 +96,8 @@ static void Mini_LutPush( Mini_Lut_t * p, int nVars, int * pVars, unsigned * pTr
         else
             Mini_LutGrow( p, 2 * p->nCap );
     }
+    for ( i = 0; i < nVars; i++ )
+        assert( pVars[i] >= 0 && pVars[i] < p->nSize );
     for ( i = 0; i < nVars; i++ )
         p->pArray[p->LutSize * p->nSize + i] = pVars[i];
     for ( ; i < p->LutSize; i++ )