diff --git a/frankenphp.go b/frankenphp.go
index 6888cad1..737874d8 100644
--- a/frankenphp.go
+++ b/frankenphp.go
@@ -481,14 +481,43 @@ func go_apache_request_headers(threadIndex C.uintptr_t) (*C.go_string, C.size_t)
 }
 
 func addHeader(fc *frankenPHPContext, cString *C.char, length C.int) {
-	parts := strings.SplitN(C.GoStringN(cString, length), ": ", 2)
-	if len(parts) != 2 {
-		fc.logger.LogAttrs(context.Background(), slog.LevelDebug, "invalid header", slog.String("header", parts[0]))
-
+	key, val := splitRawHeader(cString, int(length))
+	if key == "" {
+		fc.logger.LogAttrs(context.Background(), slog.LevelDebug, "invalid header", slog.String("header", C.GoStringN(cString, length)))
 		return
 	}
+	fc.responseWriter.Header().Add(key, val)
+}
 
-	fc.responseWriter.Header().Add(parts[0], parts[1])
+// split the raw header coming from C with minimal allocations
+func splitRawHeader(rawHeader *C.char, length int) (string, string) {
+	buf := unsafe.Slice((*byte)(unsafe.Pointer(rawHeader)), length)
+
+	// Search for the colon in 'Header-Key: value'
+	var i int
+	for i = 0; i < length; i++ {
+		if buf[i] == ':' {
+			break
+		}
+	}
+
+	if i == length {
+		return "", "" // No colon found, invalid header
+	}
+
+	headerKey := C.GoStringN(rawHeader, C.int(i))
+
+	// skip whitespaces after the colon
+	j := i + 1
+	for j < length && buf[j] == ' ' {
+		j++
+	}
+
+	// anything left is the header value
+	valuePtr := (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(rawHeader)) + uintptr(j)))
+	headerValue := C.GoStringN(valuePtr, C.int(length-j))
+
+	return headerKey, headerValue
 }
 
 //export go_write_headers
diff --git a/frankenphp_test.go b/frankenphp_test.go
index 917c931a..24241e05 100644
--- a/frankenphp_test.go
+++ b/frankenphp_test.go
@@ -242,6 +242,7 @@ func testHeaders(t *testing.T, opts *testOptions) {
 		assert.Equal(t, 201, resp.StatusCode)
 		assert.Equal(t, "bar", resp.Header.Get("Foo"))
 		assert.Equal(t, "bar2", resp.Header.Get("Foo2"))
+		assert.Equal(t, "bar3", resp.Header.Get("Foo3"), "header without whitespace after colon")
 		assert.Empty(t, resp.Header.Get("Invalid"))
 		assert.Equal(t, fmt.Sprintf("%d", i), resp.Header.Get("I"))
 	}, opts)
diff --git a/testdata/headers.php b/testdata/headers.php
index 75d141ea..6728175d 100644
--- a/testdata/headers.php
+++ b/testdata/headers.php
@@ -5,6 +5,7 @@ require_once __DIR__.'/_executor.php';
 return function () {
     header('Foo: bar');
     header('Foo2: bar2');
+    header('Foo3:bar3'); // no space after colon (also valid, not recommended)
     header('Invalid');
     header('I: ' . ($_GET['i'] ?? 'i not set'));
     http_response_code(201);