diff --git a/testsuite/tools/simplify-data-3to4/actionbar.expected b/testsuite/tools/simplify-data-3to4/actionbar.expected
index 8afe4c83fe..f356da78aa 100644
--- a/testsuite/tools/simplify-data-3to4/actionbar.expected
+++ b/testsuite/tools/simplify-data-3to4/actionbar.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkActionBar">
     <property name="visible">0</property>
     <child type="start">
diff --git a/testsuite/tools/simplify-data-3to4/actionbar.ui b/testsuite/tools/simplify-data-3to4/actionbar.ui
index efae5962d9..7128aa8945 100644
--- a/testsuite/tools/simplify-data-3to4/actionbar.ui
+++ b/testsuite/tools/simplify-data-3to4/actionbar.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk+" version="3.0"/>
   <object class="GtkActionBar">
     <child>
       <object class="GtkButton" id="button">
diff --git a/testsuite/tools/simplify-data-3to4/assistant.expected b/testsuite/tools/simplify-data-3to4/assistant.expected
index 906c68c4b2..532abbb701 100644
--- a/testsuite/tools/simplify-data-3to4/assistant.expected
+++ b/testsuite/tools/simplify-data-3to4/assistant.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkAssistant" id="window1">
     <child>
       <object class="GtkAssistantPage">
diff --git a/testsuite/tools/simplify-data-3to4/assistant.ui b/testsuite/tools/simplify-data-3to4/assistant.ui
index e731f51245..83d1dfe908 100644
--- a/testsuite/tools/simplify-data-3to4/assistant.ui
+++ b/testsuite/tools/simplify-data-3to4/assistant.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkAssistant" id="window1">
     <child>
       <object class="GtkButton" id="button1">
diff --git a/testsuite/tools/simplify-data-3to4/bin.expected b/testsuite/tools/simplify-data-3to4/bin.expected
index 52b3f1c633..f6af9712b6 100644
--- a/testsuite/tools/simplify-data-3to4/bin.expected
+++ b/testsuite/tools/simplify-data-3to4/bin.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkFrame">
     <property name="visible">0</property>
     <property name="label">bla</property>
diff --git a/testsuite/tools/simplify-data-3to4/box.expected b/testsuite/tools/simplify-data-3to4/box.expected
index 6f0d194bc8..3d452aca8b 100644
--- a/testsuite/tools/simplify-data-3to4/box.expected
+++ b/testsuite/tools/simplify-data-3to4/box.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow">
     <property name="child">
       <object class="GtkBox">
diff --git a/testsuite/tools/simplify-data-3to4/box.ui b/testsuite/tools/simplify-data-3to4/box.ui
index fad61969e8..ece4ca7eee 100644
--- a/testsuite/tools/simplify-data-3to4/box.ui
+++ b/testsuite/tools/simplify-data-3to4/box.ui
@@ -1,7 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.22.2 -->
 <interface>
-  <requires lib="gtk+" version="3.0"/>
   <object class="GtkWindow">
     <child>
       <object class="GtkBox">
diff --git a/testsuite/tools/simplify-data-3to4/dialog.expected b/testsuite/tools/simplify-data-3to4/dialog.expected
index 5742f71e02..24c975fd76 100644
--- a/testsuite/tools/simplify-data-3to4/dialog.expected
+++ b/testsuite/tools/simplify-data-3to4/dialog.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <object class="GtkDialog">
+  <requires lib="gtk" version="4.0"/>
   <child internal-child="content_area">
     <object class="GtkBox">
       <property name="visible">0</property>
diff --git a/testsuite/tools/simplify-data-3to4/fixed.expected b/testsuite/tools/simplify-data-3to4/fixed.expected
index 2b18a84b1b..2ba12071ed 100644
--- a/testsuite/tools/simplify-data-3to4/fixed.expected
+++ b/testsuite/tools/simplify-data-3to4/fixed.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkFixed">
     <child>
       <object class="GtkButton" id="button">
diff --git a/testsuite/tools/simplify-data-3to4/fixed.ui b/testsuite/tools/simplify-data-3to4/fixed.ui
index 699bea2e07..8eca6d0125 100644
--- a/testsuite/tools/simplify-data-3to4/fixed.ui
+++ b/testsuite/tools/simplify-data-3to4/fixed.ui
@@ -1,7 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.22.2 -->
 <interface>
-  <requires lib="gtk+" version="3.0"/>
   <object class="GtkFixed">
     <property name="visible">True</property>
     <child>
diff --git a/testsuite/tools/simplify-data-3to4/grid.expected b/testsuite/tools/simplify-data-3to4/grid.expected
index 517dcd0f1d..b2f4f733aa 100644
--- a/testsuite/tools/simplify-data-3to4/grid.expected
+++ b/testsuite/tools/simplify-data-3to4/grid.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow" id="window1">
     <property name="child">
       <object class="GtkGrid" id="grid1">
diff --git a/testsuite/tools/simplify-data-3to4/grid.ui b/testsuite/tools/simplify-data-3to4/grid.ui
index a853331dc5..110baf2d64 100644
--- a/testsuite/tools/simplify-data-3to4/grid.ui
+++ b/testsuite/tools/simplify-data-3to4/grid.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkWindow" id="window1">
     <child>
       <object class="GtkGrid" id="grid1">
diff --git a/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.expected b/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.expected
index 11a691763d..b96ec784d8 100644
--- a/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.expected
+++ b/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface domain="gtk30">
+  <requires lib="gtk" version="4.0"/>
   <template class="GtkFileChooserDialog" parent="GtkDialog">
     <property name="role">GtkFileChooserDialog</property>
     <property name="type-hint">dialog</property>
diff --git a/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.ui b/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.ui
index 9315717e79..a3027e22b5 100644
--- a/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.ui
+++ b/testsuite/tools/simplify-data-3to4/gtkfilechooserdialog.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface domain="gtk30">
-  <!-- interface-requires gtk+ 3.10 -->
   <template class="GtkFileChooserDialog" parent="GtkDialog">
     <property name="role">GtkFileChooserDialog</property>
     <property name="type-hint">dialog</property>
diff --git a/testsuite/tools/simplify-data-3to4/headerbar.expected b/testsuite/tools/simplify-data-3to4/headerbar.expected
index 5b642b28d8..c3ef9659de 100644
--- a/testsuite/tools/simplify-data-3to4/headerbar.expected
+++ b/testsuite/tools/simplify-data-3to4/headerbar.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow" id="window1">
     <child type="titlebar">
       <object class="GtkHeaderBar" id="headerbar1">
diff --git a/testsuite/tools/simplify-data-3to4/headerbar.ui b/testsuite/tools/simplify-data-3to4/headerbar.ui
index c12d3d9ed1..07dc77e73d 100644
--- a/testsuite/tools/simplify-data-3to4/headerbar.ui
+++ b/testsuite/tools/simplify-data-3to4/headerbar.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkWindow" id="window1">
     <child type="titlebar">
       <object class="GtkHeaderBar" id="headerbar1">
diff --git a/testsuite/tools/simplify-data-3to4/nm-crash.expected b/testsuite/tools/simplify-data-3to4/nm-crash.expected
index a5b531f01a..a84ba689a6 100644
--- a/testsuite/tools/simplify-data-3to4/nm-crash.expected
+++ b/testsuite/tools/simplify-data-3to4/nm-crash.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface domain="nm-applet">
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkAssistant">
     <child>
       <object class="GtkAssistantPage">
diff --git a/testsuite/tools/simplify-data-3to4/notebook.expected b/testsuite/tools/simplify-data-3to4/notebook.expected
index f0bc7f9e82..b946bbaefd 100644
--- a/testsuite/tools/simplify-data-3to4/notebook.expected
+++ b/testsuite/tools/simplify-data-3to4/notebook.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow" id="window1">
     <property name="child">
       <object class="GtkNotebook" id="notebook1">
diff --git a/testsuite/tools/simplify-data-3to4/notebook.ui b/testsuite/tools/simplify-data-3to4/notebook.ui
index ce3ce2cbad..ddf822beb8 100644
--- a/testsuite/tools/simplify-data-3to4/notebook.ui
+++ b/testsuite/tools/simplify-data-3to4/notebook.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkWindow" id="window1">
     <child>
       <object class="GtkNotebook" id="notebook1">
diff --git a/testsuite/tools/simplify-data-3to4/office-runner.expected b/testsuite/tools/simplify-data-3to4/office-runner.expected
index d6860d0fd7..799691e703 100644
--- a/testsuite/tools/simplify-data-3to4/office-runner.expected
+++ b/testsuite/tools/simplify-data-3to4/office-runner.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow" id="window1">
     <property name="border_width">12</property>
     <property name="title" translatable="yes">Office Runner</property>
diff --git a/testsuite/tools/simplify-data-3to4/office-runner.ui b/testsuite/tools/simplify-data-3to4/office-runner.ui
index 9f417cefbb..d7a7aae784 100644
--- a/testsuite/tools/simplify-data-3to4/office-runner.ui
+++ b/testsuite/tools/simplify-data-3to4/office-runner.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkWindow" id="window1">
     <property name="border_width">12</property>
     <property name="title" translatable="yes">Office Runner</property>
diff --git a/testsuite/tools/simplify-data-3to4/overlay.expected b/testsuite/tools/simplify-data-3to4/overlay.expected
index a37d2ab8b5..095475de42 100644
--- a/testsuite/tools/simplify-data-3to4/overlay.expected
+++ b/testsuite/tools/simplify-data-3to4/overlay.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkOverlay">
     <child type="overlay">
       <object class="GtkButton" id="button">
diff --git a/testsuite/tools/simplify-data-3to4/paned.expected b/testsuite/tools/simplify-data-3to4/paned.expected
index a868fd2fd4..d767086ba8 100644
--- a/testsuite/tools/simplify-data-3to4/paned.expected
+++ b/testsuite/tools/simplify-data-3to4/paned.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkPaned">
     <property name="resize-end-child">0</property>
     <property name="shrink-start-child">0</property>
diff --git a/testsuite/tools/simplify-data-3to4/popover.expected b/testsuite/tools/simplify-data-3to4/popover.expected
index 9f2cafebc7..d204fdfe4d 100644
--- a/testsuite/tools/simplify-data-3to4/popover.expected
+++ b/testsuite/tools/simplify-data-3to4/popover.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkPopover" id="popover">
     <property name="autohide">0</property>
   </object>
diff --git a/testsuite/tools/simplify-data-3to4/scale.expected b/testsuite/tools/simplify-data-3to4/scale.expected
index 20e71ab9da..7a612ac8fe 100644
--- a/testsuite/tools/simplify-data-3to4/scale.expected
+++ b/testsuite/tools/simplify-data-3to4/scale.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkScale">
     <property name="draw-value">1</property>
     <property name="visible">0</property>
diff --git a/testsuite/tools/simplify-data-3to4/stack.expected b/testsuite/tools/simplify-data-3to4/stack.expected
index 611d20edf8..b8f1320c14 100644
--- a/testsuite/tools/simplify-data-3to4/stack.expected
+++ b/testsuite/tools/simplify-data-3to4/stack.expected
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkWindow" id="window1">
     <property name="child">
       <object class="GtkBox" id="box1">
diff --git a/testsuite/tools/simplify-data-3to4/stack.ui b/testsuite/tools/simplify-data-3to4/stack.ui
index e3133911ca..833d0d0a63 100644
--- a/testsuite/tools/simplify-data-3to4/stack.ui
+++ b/testsuite/tools/simplify-data-3to4/stack.ui
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <!-- interface-requires gtk+ 3.0 -->
   <object class="GtkWindow" id="window1">
     <child>
       <object class="GtkBox" id="box1">
diff --git a/testsuite/tools/simplify-data-3to4/toolbar.expected b/testsuite/tools/simplify-data-3to4/toolbar.expected
index 8fa1e1edfc..558022d325 100644
--- a/testsuite/tools/simplify-data-3to4/toolbar.expected
+++ b/testsuite/tools/simplify-data-3to4/toolbar.expected
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface>
-  <requires lib="gtk" version="3.0"/>
+  <requires lib="gtk" version="4.0"/>
   <object class="GtkBox">
     <style>
       <class name="toolbar"/>
diff --git a/testsuite/tools/validate-data/invalid5.expected b/testsuite/tools/validate-data/invalid5.expected
new file mode 100644
index 0000000000..efe4d76422
--- /dev/null
+++ b/testsuite/tools/validate-data/invalid5.expected
@@ -0,0 +1 @@
+invalid5.ui:3:1 Required GTK version 5.10, current version is 3.99
diff --git a/testsuite/tools/validate-data/invalid5.ui b/testsuite/tools/validate-data/invalid5.ui
new file mode 100644
index 0000000000..f438790a4c
--- /dev/null
+++ b/testsuite/tools/validate-data/invalid5.ui
@@ -0,0 +1,3 @@
+<interface>
+  <requires lib="gtk" version="5.10"/>
+</interface>
diff --git a/testsuite/tools/validate-data/valid3.expected b/testsuite/tools/validate-data/valid3.expected
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/testsuite/tools/validate-data/valid3.ui b/testsuite/tools/validate-data/valid3.ui
new file mode 100644
index 0000000000..53d335aaec
--- /dev/null
+++ b/testsuite/tools/validate-data/valid3.ui
@@ -0,0 +1,5 @@
+<interface>
+  <requires lib="gtk" version="3.99"/>
+  <object class="GtkWindow">
+  </object>
+</interface>
diff --git a/testsuite/tools/validate-data/valid4.expected b/testsuite/tools/validate-data/valid4.expected
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/testsuite/tools/validate-data/valid4.ui b/testsuite/tools/validate-data/valid4.ui
new file mode 100644
index 0000000000..d913a7e598
--- /dev/null
+++ b/testsuite/tools/validate-data/valid4.ui
@@ -0,0 +1,5 @@
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkWindow">
+  </object>
+</interface>