diff --git a/autotests/ktimecomboboxtest.h b/autotests/ktimecomboboxtest.h
--- a/autotests/ktimecomboboxtest.h
+++ b/autotests/ktimecomboboxtest.h
@@ -36,6 +36,7 @@
     void testTimeList();
     void testOptions();
     void testDisplayFormat();
+    void testMask();
 
 private:
 
diff --git a/autotests/ktimecomboboxtest.cpp b/autotests/ktimecomboboxtest.cpp
--- a/autotests/ktimecomboboxtest.cpp
+++ b/autotests/ktimecomboboxtest.cpp
@@ -184,3 +184,27 @@
     QCOMPARE(m_combo->displayFormat(), format);
     delete m_combo;
 }
+
+void KTimeComboBoxTest::testMask()
+{
+    // Store the current locale, and set to one which reproduces the bug.
+    QLocale currentLocale;
+
+    // Test that the line edit input mask AM/PM portion gets correctly
+    // replaced with aa.
+    QLocale::setDefault(QLocale(QLocale::English, QLocale::Australia));
+    m_combo = new KTimeComboBox(nullptr);
+    QString mask = m_combo->lineEdit()->inputMask();
+    QCOMPARE(mask.contains(QLatin1String("aa")), true);
+    delete m_combo;
+
+    // For 24 hour time formats, no am/pm specifier in mask
+    QLocale::setDefault(QLocale(QLocale::Norwegian, QLocale::Norway));
+    m_combo = new KTimeComboBox(nullptr);
+    mask = m_combo->lineEdit()->inputMask();
+    QCOMPARE(mask.contains(QLatin1String("aa")), false);
+    delete m_combo;
+
+    // Restore the previous locale
+    QLocale::setDefault(currentLocale);
+}
diff --git a/src/ktimecombobox.cpp b/src/ktimecombobox.cpp
--- a/src/ktimecombobox.cpp
+++ b/src/ktimecombobox.cpp
@@ -105,10 +105,27 @@
     null.replace(locale.toString(56), QLatin1String(""));
     mask.replace(locale.toString(789), QLatin1String("900"));
     null.replace(locale.toString(789), QLatin1String(""));
-    if (format.contains(QLatin1String("ap")) ||
-            format.contains(QLatin1String("AP"))) {
+
+    // See if this time format contains a specifier for
+    // AM/PM, regardless of case.
+    int ampmPos = format.indexOf(QLatin1String("AP"), 0, Qt::CaseInsensitive);
+
+    if (ampmPos != -1) {
+        // Get the locale aware am/pm strings
         QString am = locale.amText();
         QString pm = locale.pmText();
+
+        // Convert the am/pm strings to the same case
+        // as the input format. This is necessary to
+        // provide a correct mask to the line edit.
+        if (format[ampmPos].isUpper()) {
+            am = am.toUpper();
+            pm = pm.toUpper();
+        } else {
+            am = am.toLower();
+            pm = pm.toLower();
+        }
+
         int ampmLen = qMax(am.length(), pm.length());
         QString ampmMask;
         for (int i = 0; i < ampmLen; ++i) {