diff --git a/kcms/fonts/fonts.cpp b/kcms/fonts/fonts.cpp
--- a/kcms/fonts/fonts.cpp
+++ b/kcms/fonts/fonts.cpp
@@ -608,13 +608,23 @@
     int ret = KFontDialog::getFontDiff(font, fontDiffFlags, KFontChooser::NoDisplayFlags);
 
     if (ret == KDialog::Accepted && fontDiffFlags) {
-        m_settings->setFont(applyFontDiff(m_settings->font(), font, fontDiffFlags));
-        m_settings->setMenuFont(applyFontDiff(m_settings->menuFont(), font, fontDiffFlags));
-        m_settings->setToolBarFont(applyFontDiff(m_settings->toolBarFont(), font, fontDiffFlags));
-        m_settings->setActiveFont(applyFontDiff(m_settings->activeFont(), font, fontDiffFlags));
-        m_settings->setSmallestReadableFont(applyFontDiff(m_settings->smallestReadableFont(), font, fontDiffFlags));
+        if (!m_settings->isImmutable("font")) {
+            m_settings->setFont(applyFontDiff(m_settings->font(), font, fontDiffFlags));
+        }
+        if (!m_settings->isImmutable("menuFont")) {
+            m_settings->setMenuFont(applyFontDiff(m_settings->menuFont(), font, fontDiffFlags));
+        }
+        if (!m_settings->isImmutable("toolBarFont")) {
+            m_settings->setToolBarFont(applyFontDiff(m_settings->toolBarFont(), font, fontDiffFlags));
+        }
+        if (!m_settings->isImmutable("activeFont")) {
+            m_settings->setActiveFont(applyFontDiff(m_settings->activeFont(), font, fontDiffFlags));
+        }
+        if (!m_settings->isImmutable("smallestReadableFont")) {
+            m_settings->setSmallestReadableFont(applyFontDiff(m_settings->smallestReadableFont(), font, fontDiffFlags));
+        }
         const QFont adjustedFont = applyFontDiff(m_settings->fixed(), font, fontDiffFlags);
-        if (QFontInfo(adjustedFont).fixedPitch()) {
+        if (QFontInfo(adjustedFont).fixedPitch() && !m_settings->isImmutable("fixed")) {
             m_settings->setFixed(adjustedFont);
         }
     }
diff --git a/kcms/fonts/package/contents/ui/main.qml b/kcms/fonts/package/contents/ui/main.qml
--- a/kcms/fonts/package/contents/ui/main.qml
+++ b/kcms/fonts/package/contents/ui/main.qml
@@ -55,38 +55,50 @@
                 text: i18n("&Adjust All Fonts...")
 
                 onClicked: kcm.adjustAllFonts();
+                enabled: !kcm.fontsSettings.isImmutable("font")
+                        || !kcm.fontsSettings.isImmutable("fixed")
+                        || !kcm.fontsSettings.isImmutable("smallestReadableFont")
+                        || !kcm.fontsSettings.isImmutable("toolBarFont")
+                        || !kcm.fontsSettings.isImmutable("menuFont")
+                        || !kcm.fontsSettings.isImmutable("activeFont")
             }
 
             FontWidget {
                 id: generalFontWidget
                 label: i18n("General:")
                 category: "font"
                 font: kcm.fontsSettings.font
+                enabled: !kcm.fontsSettings.isImmutable("font")
             }
             FontWidget {
                 label: i18n("Fixed width:")
                 category: "fixed"
                 font: kcm.fontsSettings.fixed
+                enabled: !kcm.fontsSettings.isImmutable("fixed")
             }
             FontWidget {
                 label: i18n("Small:")
                 category: "smallestReadableFont"
                 font: kcm.fontsSettings.smallestReadableFont
+                enabled: !kcm.fontsSettings.isImmutable("smallestReadableFont")
             }
             FontWidget {
                 label: i18n("Toolbar:")
                 category: "toolBarFont"
                 font: kcm.fontsSettings.toolBarFont
+                enabled: !kcm.fontsSettings.isImmutable("toolBarFont")
             }
             FontWidget {
                 label: i18n("Menu:")
                 category: "menuFont"
                 font: kcm.fontsSettings.menuFont
+                enabled: !kcm.fontsSettings.isImmutable("menuFont")
             }
             FontWidget {
                 label: i18n("Window title:")
                 category: "activeFont"
                 font: kcm.fontsSettings.activeFont
+                enabled: !kcm.fontsSettings.isImmutable("activeFont")
             }
 
             Kirigami.Separator {