diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7c36733..190aaff 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -8,7 +8,7 @@ jobs:
   Tests:
     strategy:
       matrix:
-        go-version: [1.18.x, 1.19.x, 1.20.x]
+        go-version: [1.19.x, 1.20.x]
         platform: [ubuntu-latest, windows-latest, macos-latest]
     runs-on: ${{ matrix.platform }}
     steps:
diff --git a/bytes.go b/bytes.go
index e5b5488..e24b5fe 100644
--- a/bytes.go
+++ b/bytes.go
@@ -4,7 +4,7 @@
 
 package utils
 
-// ToLowerBytes converts ascii slice to lower-case in-place.
+// ToLowerBytes converts ascii slice to lower-case
 func ToLowerBytes(b []byte) []byte {
 	for i := 0; i < len(b); i++ {
 		b[i] = toLowerTable[b[i]]
@@ -12,7 +12,7 @@ func ToLowerBytes(b []byte) []byte {
 	return b
 }
 
-// ToUpperBytes converts ascii slice to upper-case in-place.
+// ToUpperBytes converts ascii slice to upper-case
 func ToUpperBytes(b []byte) []byte {
 	for i := 0; i < len(b); i++ {
 		b[i] = toUpperTable[b[i]]
diff --git a/convert.go b/convert.go
index 9b456f1..36f015d 100644
--- a/convert.go
+++ b/convert.go
@@ -13,6 +13,8 @@ import (
 	"unsafe"
 )
 
+const MaxStringLen = 0x7fff0000 // Maximum string length for UnsafeBytes. (decimal: 2147418112)
+
 // #nosec G103
 // UnsafeString returns a string pointer without allocation
 func UnsafeString(b []byte) string {
@@ -20,14 +22,16 @@ func UnsafeString(b []byte) string {
 }
 
 // #nosec G103
-// UnsafeBytes returns a byte pointer without allocation
-func UnsafeBytes(s string) (bs []byte) {
-	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
-	bh := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
-	bh.Data = sh.Data
-	bh.Len = sh.Len
-	bh.Cap = sh.Len
-	return
+// UnsafeBytes returns a byte pointer without allocation.
+// String length shouldn't be more than 2147418112.
+func UnsafeBytes(s string) []byte {
+	if s == "" {
+		return nil
+	}
+
+	return (*[MaxStringLen]byte)(unsafe.Pointer(
+		(*reflect.StringHeader)(unsafe.Pointer(&s)).Data),
+	)[:len(s):len(s)]
 }
 
 // CopyString copies a string to make it immutable
diff --git a/http.go b/http.go
index 7aacd39..b2b0e6b 100644
--- a/http.go
+++ b/http.go
@@ -4,24 +4,37 @@
 
 package utils
 
-import "strings"
+import (
+	"mime"
+	"strings"
+)
 
 const MIMEOctetStream = "application/octet-stream"
 
 // GetMIME returns the content-type of a file extension
-func GetMIME(extension string) (mime string) {
+func GetMIME(extension string) string {
 	if len(extension) == 0 {
-		return mime
+		return ""
 	}
+	var foundMime string
 	if extension[0] == '.' {
-		mime = mimeExtensions[extension[1:]]
+		foundMime = mimeExtensions[extension[1:]]
 	} else {
-		mime = mimeExtensions[extension]
+		foundMime = mimeExtensions[extension]
 	}
-	if len(mime) == 0 {
-		return MIMEOctetStream
+
+	if len(foundMime) == 0 {
+		if extension[0] != '.' {
+			foundMime = mime.TypeByExtension("." + extension)
+		} else {
+			foundMime = mime.TypeByExtension(extension)
+		}
+
+		if foundMime == "" {
+			return MIMEOctetStream
+		}
 	}
-	return mime
+	return foundMime
 }
 
 // ParseVendorSpecificContentType check if content type is vendor specific and
diff --git a/http_test.go b/http_test.go
index e06e890..d826bfc 100644
--- a/http_test.go
+++ b/http_test.go
@@ -25,9 +25,18 @@ func Test_GetMIME(t *testing.T) {
 
 	res = GetMIME("unknown")
 	require.Equal(t, MIMEOctetStream, res)
+
 	// empty case
 	res = GetMIME("")
 	require.Equal(t, "", res)
+
+	err := mime.AddExtensionType(".mjs", "application/javascript")
+	if err == nil {
+		res = GetMIME(".mjs")
+		require.Equal(t, "application/javascript", res)
+	}
+	require.NoError(t, err)
+
 }
 
 // go test -v -run=^$ -bench=Benchmark_GetMIME -benchmem -count=2
diff --git a/ips.go b/ips.go
index 6d24464..333054f 100644
--- a/ips.go
+++ b/ips.go
@@ -26,7 +26,7 @@ func IsIPv4(s string) bool {
 			}
 		}
 
-		if ci == 0 || n > 0xFF || (ci > 1 && s[0] == '0') {
+		if ci == 0 || (ci > 1 && s[0] == '0') {
 			return false
 		}
 
diff --git a/ips_test.go b/ips_test.go
index ce9109c..7c392eb 100644
--- a/ips_test.go
+++ b/ips_test.go
@@ -27,6 +27,12 @@ func Test_IsIPv4(t *testing.T) {
 	require.Equal(t, false, IsIPv4(""))
 	require.Equal(t, false, IsIPv4("2345:0425:2CA1::0567:5673:23b5"))
 	require.Equal(t, false, IsIPv4("invalid"))
+	require.Equal(t, false, IsIPv4("189.12.34.260"))
+	require.Equal(t, false, IsIPv4("189.12.260.260"))
+	require.Equal(t, false, IsIPv4("189.260.260.260"))
+	require.Equal(t, false, IsIPv4("999.999.999.999"))
+	require.Equal(t, false, IsIPv4("9999.9999.9999.9999"))
+
 }
 
 // go test -v -run=^$ -bench=UnsafeString -benchmem -count=2