diff --git a/common/bytes.go b/common/bytes.go
index 457aea96bf..ba00e8a4b2 100644
--- a/common/bytes.go
+++ b/common/bytes.go
@@ -53,25 +53,19 @@ func CopyBytes(b []byte) (copiedBytes []byte) {
 	return
 }
 
-func HasHexPrefix(str string) bool {
-	l := len(str)
-	return l >= 2 && (str[0:2] == "0x" || str[0:2] == "0X")
+func hasHexPrefix(str string) bool {
+	return len(str) >= 2 && str[0] == '0' && (str[1] == 'x' || str[1] == 'X')
 }
 
 func isHexCharacter(c byte) bool {
-	return ('0' <= c && c <= '9') ||
-		('a' <= c && c <= 'f') ||
-		('A' <= c && c <= 'F')
+	return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') || ('A' <= c && c <= 'F')
 }
 
-func IsHex(str string) bool {
-	if HasHexPrefix(str) {
-		str = str[2:]
-	}
+func isHex(str string) bool {
 	if len(str)%2 != 0 {
 		return false
 	}
-	for _, c := range []byte(src) {
+	for _, c := range []byte(str) {
 		if !isHexCharacter(c) {
 			return false
 		}
diff --git a/common/bytes_test.go b/common/bytes_test.go
index 081e039dd6..3f99ba02f6 100644
--- a/common/bytes_test.go
+++ b/common/bytes_test.go
@@ -34,28 +34,6 @@ func (s *BytesSuite) TestCopyBytes(c *checker.C) {
 	c.Assert(res1, checker.DeepEquals, exp1)
 }
 
-func (s *BytesSuite) TestIsHex(c *checker.C) {
-	data1 := "a9e67e"
-	exp1 := true
-	res1 := IsHex(data1)
-	c.Assert(res1, checker.DeepEquals, exp1)
-
-	data2 := "0xa9e67e00"
-	exp2 := true
-	res2 := IsHex(data2)
-	c.Assert(res2, checker.DeepEquals, exp2)
-
-	data3 := "0xa9e67e001"
-	exp3 := false
-	res3 := IsHex(data3)
-	c.Assert(res3, checker.DeepEquals, exp3)
-
-	data4 := "0xHELLO_MY_NAME_IS_STEVEN_@#$^&*"
-	exp4 := false
-	res4 := IsHex(data4)
-	c.Assert(res4, checker.DeepEquals, exp4)
-}
-
 func (s *BytesSuite) TestLeftPadBytes(c *checker.C) {
 	val1 := []byte{1, 2, 3, 4}
 	exp1 := []byte{0, 0, 0, 0, 1, 2, 3, 4}
@@ -87,6 +65,27 @@ func TestFromHex(t *testing.T) {
 	}
 }
 
+func TestIsHex(t *testing.T) {
+	tests := []struct {
+		input string
+		ok    bool
+	}{
+		{"", true},
+		{"0", false},
+		{"00", true},
+		{"a9e67e", true},
+		{"A9E67E", true},
+		{"0xa9e67e", false},
+		{"a9e67e001", false},
+		{"0xHELLO_MY_NAME_IS_STEVEN_@#$^&*", false},
+	}
+	for _, test := range tests {
+		if ok := isHex(test.input); ok != test.ok {
+			t.Error("isHex(%q) = %v, want %v", test.input, ok, test.ok)
+		}
+	}
+}
+
 func TestFromHexOddLength(t *testing.T) {
 	input := "0x1"
 	expected := []byte{1}
diff --git a/common/types.go b/common/types.go
index 670f0cf2f3..fdc67480c2 100644
--- a/common/types.go
+++ b/common/types.go
@@ -150,10 +150,10 @@ func HexToAddress(s string) Address    { return BytesToAddress(FromHex(s)) }
 // IsHexAddress verifies whether a string can represent a valid hex-encoded
 // Ethereum address or not.
 func IsHexAddress(s string) bool {
-	if HasHexPrefix(s) {
-		return len(s) == 2+2*AddressLength && IsHex(s[2:])
+	if hasHexPrefix(s) {
+		s = s[2:]
 	}
-	return len(s) == 2*AddressLength && IsHex(s)
+	return len(s) == 2*AddressLength && isHex(s)
 }
 
 // Get the string representation of the underlying address