diff --git a/src/libs/utils/mimetypes/mimetypeparser.cpp b/src/libs/utils/mimetypes/mimetypeparser.cpp
index 643b9b192d1..ab43ffd3556 100644
--- a/src/libs/utils/mimetypes/mimetypeparser.cpp
+++ b/src/libs/utils/mimetypes/mimetypeparser.cpp
@@ -162,7 +162,8 @@ static bool parseNumber(const QString &n, int *target, QString *errorMessage)
     bool ok;
     *target = n.toInt(&ok);
     if (!ok) {
-        *errorMessage = QString::fromLatin1("Not a number '%1'.").arg(n);
+        if (errorMessage)
+            *errorMessage = QString::fromLatin1("Not a number '%1'.").arg(n);
         return false;
     }
     return true;