diff --git a/internal/useragent/useragent.go b/internal/useragent/useragent.go
index 66b6a5b..2079a7d 100644
--- a/internal/useragent/useragent.go
+++ b/internal/useragent/useragent.go
@@ -36,7 +36,7 @@ func buildSourceTagField(userAgent string) string {
 	// Limit charset to [a-z0-9_ ]
 	var strBldr strings.Builder
 	for _, char := range userAgent {
-		if (char >= 'a' && char <= 'z') || (char >= '0' && char <= '9') || char == '_' || char == ' ' {
+		if (char >= 'a' && char <= 'z') || (char >= '0' && char <= '9') || char == '_' || char == ' ' || char == ':' {
 			strBldr.WriteRune(char)
 		}
 	}
diff --git a/internal/useragent/useragent_test.go b/internal/useragent/useragent_test.go
index 16bf7f0..f16798c 100644
--- a/internal/useragent/useragent_test.go
+++ b/internal/useragent/useragent_test.go
@@ -78,4 +78,9 @@ func TestBuildUserAgentSourceTagIsNormalized(t *testing.T) {
 	if !strings.Contains(result, "source_tag=my_source_tag") {
 		t.Errorf("BuildUserAgent(\"%s\"): expected user-agent to contain 'source_tag=my_source_tag_123', but got %s", sourceTag, result)
 	}
+
+	sourceTag = "   My Source Tag  123 : !! "
+	if !strings.Contains(result, "source_tag=my_source_tag:") {
+		t.Errorf("BuildUserAgent(\"%s\"): expected user-agent to contain 'source_tag=my_source_tag_123', but got %s", sourceTag, result)
+	}
 }