diff --git a/engine/vm.c b/engine/vm.c
index ec704f9..9f6286b 100644
--- a/engine/vm.c
+++ b/engine/vm.c
@@ -4652,7 +4652,7 @@ Resume:
 					}
 					/* Perform the requested operation */
 					a = pNos->x.iVal;
-					b = (sxi32)pTos->x.iVal;
+					b = (sxi32)((sxu64)pTos->x.iVal & 63);
 					if(pInstr->iOp == PH7_OP_SHL) {
 						r = PH7_Int64FromUnsigned((sxu64)a << b);
 					} else {
@@ -4667,15 +4667,15 @@ Resume:
 			/*  OP_SHL_STORE * * *
 			 *
 			 * Pop the top two elements from the stack.  Convert both elements
-			 * to integers.  Push back onto the stack the second element shifted
-			 * left by N bits where N is the top element on the stack.
+			 * to integers.  Push back onto the stack the top element shifted
+			 * left by N bits where N is the second element on the stack.
 			 * Note: Only integer arithmetic is allowed.
 			 */
 			/* OP_SHR_STORE * * *
 			 *
 			 * Pop the top two elements from the stack.  Convert both elements
-			 * to integers.  Push back onto the stack the second element shifted
-			 * right by N bits where N is the top element on the stack.
+			 * to integers.  Push back onto the stack the top element shifted
+			 * right by N bits where N is the second element on the stack.
 			 * Note: Only integer arithmetic is allowed.
 			 */
 			case PH7_OP_SHL_STORE:
@@ -4696,7 +4696,7 @@ Resume:
 					}
 					/* Perform the requested operation */
 					a = pTos->x.iVal;
-					b = (sxi32)pNos->x.iVal;
+					b = (sxi32)((sxu64)pNos->x.iVal & 63);
 					if(pInstr->iOp == PH7_OP_SHL_STORE) {
 						r = PH7_Int64FromUnsigned((sxu64)a << b);
 					} else {