diff --git a/.changelog/0e1f4e3313a449c8b2230d6cc756ef18.json b/.changelog/0e1f4e3313a449c8b2230d6cc756ef18.json
new file mode 100644
index 00000000000..aaa553a117e
--- /dev/null
+++ b/.changelog/0e1f4e3313a449c8b2230d6cc756ef18.json
@@ -0,0 +1,8 @@
+{
+    "id": "0e1f4e33-13a4-49c8-b223-0d6cc756ef18",
+    "type": "bugfix",
+    "description": "Fix subproperty performance regression",
+    "modules": [
+        "internal/ini"
+    ]
+}
\ No newline at end of file
diff --git a/internal/ini/literal_tokens.go b/internal/ini/literal_tokens.go
index a24903202ac..f0372a68ef0 100644
--- a/internal/ini/literal_tokens.go
+++ b/internal/ini/literal_tokens.go
@@ -133,6 +133,17 @@ func newLitToken(b []rune) (Token, int, error) {
 	return token, n, err
 }
 
+// replace with slices.Contains when Go 1.21
+// is min supported Go version in the SDK
+func containsRune(runes []rune, val rune) bool {
+	for i := range runes {
+		if val == runes[i] {
+			return true
+		}
+	}
+	return false
+}
+
 func isSubProperty(runes []rune) bool {
 	// needs at least
 	// (1) newline (2) whitespace (3) literal
@@ -141,10 +152,7 @@ func isSubProperty(runes []rune) bool {
 	}
 
 	// must have an equal expression
-	split := strings.FieldsFunc(string(runes), func(r rune) bool {
-		return isOp([]rune{r})
-	})
-	if len(split) < 2 {
+	if !containsRune(runes, '=') && !containsRune(runes, ':') {
 		return false
 	}
 
@@ -156,7 +164,6 @@ func isSubProperty(runes []rune) bool {
 	if err != nil {
 		return false
 	}
-
 	// whitespace must follow newline
 	return isWhitespace(runes[n])
 }