diff --git a/gtk4/src/main/java/io/github/jwharm/javagi/Interop.java b/gtk4/src/main/java/io/github/jwharm/javagi/Interop.java
index 78a15f89..65d34616 100644
--- a/gtk4/src/main/java/io/github/jwharm/javagi/Interop.java
+++ b/gtk4/src/main/java/io/github/jwharm/javagi/Interop.java
@@ -503,6 +503,9 @@ private Object unwrapJavagiTypes(Object o) {
             if (o == null) {
                 return MemoryAddress.NULL;
             }
+            if (o instanceof Boolean bool) {
+                return bool.booleanValue() ? 1 : 0;
+            }
             if (o instanceof Proxy proxy) {
                 return proxy.handle();
             }