diff --git a/Game/scripts/server_config.gd b/Game/scripts/server_config.gd
index b9264e5d..0867b3e8 100644
--- a/Game/scripts/server_config.gd
+++ b/Game/scripts/server_config.gd
@@ -263,7 +263,7 @@ func _validate() -> void:
 			if String(values[key]).is_empty():
 				errors.append("--allocated-mode requires --%s" % key)
 		var digest := String(values["server-image-digest"])
-		if not digest.begins_with("sha256:") or digest.length() != 71:
+		if not _is_sha256_digest(digest):
 			errors.append("--server-image-digest must be sha256:<64 hex characters>")
 		var transport := String(values["transport"])
 		if not transport in ["steam_sdr", "enet"]:
@@ -273,6 +273,15 @@ func _validate() -> void:
 			errors.append("--region must be EU or NA, got '%s'" % region)
 
 
+static func _is_sha256_digest(value: String) -> bool:
+	if not value.begins_with("sha256:") or value.length() != 71:
+		return false
+	for c in value.substr(7):
+		if not c.to_lower() in "0123456789abcdef":
+			return false
+	return true
+
+
 static func _kind_name(kind: int) -> String:
 	match kind:
 		Kind.BOOL: return "bool"