diff --git a/core/vm/contracts.go b/core/vm/contracts.go
index 928b5511ab..0c53b9d2c5 100644
--- a/core/vm/contracts.go
+++ b/core/vm/contracts.go
@@ -614,11 +614,19 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
 }
 
 func (c *bigModExp) Run(input []byte) ([]byte, error) {
-	var (
-		baseLen = new(uint256.Int).SetBytes(getData(input, 0, 32)).Uint64()
-		expLen  = new(uint256.Int).SetBytes(getData(input, 32, 32)).Uint64()
-		modLen  = new(uint256.Int).SetBytes(getData(input, 64, 32)).Uint64()
-	)
+	// Extract lengths - they're 32-byte big-endian integers
+	// with the actual uint64 value in the last 8 bytes
+	var baseLen, expLen, modLen uint64
+	if len(input) >= 32 {
+		baseLen = binary.BigEndian.Uint64(input[24:32])
+	}
+	if len(input) >= 64 {
+		expLen = binary.BigEndian.Uint64(input[56:64])
+	}
+	if len(input) >= 96 {
+		modLen = binary.BigEndian.Uint64(input[88:96])
+	}
+
 	if len(input) > 96 {
 		input = input[96:]
 	} else {