diff --git a/godot-bindings/src/godot_exe.rs b/godot-bindings/src/godot_exe.rs
index 495989e0b..dfb5a9dd6 100644
--- a/godot-bindings/src/godot_exe.rs
+++ b/godot-bindings/src/godot_exe.rs
@@ -56,18 +56,16 @@ pub fn write_gdextension_headers(
     watch: &mut StopWatch,
 ) {
     // None=(unknown, no engine), Some=(version of Godot). Later verified by header itself.
-    let is_engine_4_0;
-    if is_h_provided {
-        is_engine_4_0 = None;
-    } else {
+    // Even though we don't support 4.0 anymore, we still detect it, for better error messages.
+    if !is_h_provided {
         // No external C header file: Godot binary is present, we use it to dump C header
         let godot_bin = locate_godot_binary();
         rerun_on_changed(&godot_bin);
         watch.record("locate_godot");
 
-        // Regenerate API JSON if first time or Godot version is different
-        let version = read_godot_version(&godot_bin);
-        is_engine_4_0 = Some(version.major == 4 && version.minor == 0);
+        // Regenerate API JSON if first time or Godot version is different.
+        // Note: read_godot_version() already panics if 4.0 is still in use; no need to check again.
+        let _version = read_godot_version(&godot_bin);
 
         // if !c_header_path.exists() || has_version_changed(&version) {
         dump_header_file(&godot_bin, inout_h_path);
@@ -79,7 +77,7 @@ pub fn write_gdextension_headers(
     // Listening to changes on files that are generated by this build step cause an infinite loop with cargo watch of
     // build -> detect change -> rebuild -> detect change -> ...
     // rerun_on_changed(inout_h_path);
-    patch_c_header(inout_h_path, is_engine_4_0);
+    patch_c_header(inout_h_path);
     watch.record("patch_header_h");
 
     generate_rust_binding(inout_h_path, out_rs_path);
@@ -117,7 +115,13 @@ pub(crate) fn read_godot_version(godot_bin: &Path) -> GodotVersion {
             assert_eq!(
                 parsed.major,
                 4,
-                "Only Godot versions >= 4.0 are supported; found version {}.",
+                "Only Godot versions with major version 4 are supported; found version {}.",
+                stdout.trim()
+            );
+
+            assert!(
+                parsed.minor > 0,
+                "Godot 4.0 is no longer supported by godot-rust; found version {}.",
                 stdout.trim()
             );
 
@@ -158,35 +162,23 @@ fn dump_header_file(godot_bin: &Path, out_file: &Path) {
     println!("Generated {}/gdextension_interface.h.", cwd.display());
 }
 
-fn patch_c_header(inout_h_path: &Path, is_engine_4_0: Option<bool>) {
+fn patch_c_header(inout_h_path: &Path) {
     // The C header path *must* be passed in by the invoking crate, as the path cannot be relative to this crate.
     // Otherwise, it can be something like `/home/runner/.cargo/git/checkouts/gdext-76630c89719e160c/efd3b94/godot-bindings`.
 
-    println!(
-        "Patch C header '{}' (is_engine_4_0={is_engine_4_0:?})...",
-        inout_h_path.display()
-    );
+    println!("Patch C header '{}'...", inout_h_path.display());
 
     let mut c = fs::read_to_string(inout_h_path)
         .unwrap_or_else(|_| panic!("failed to read C header file {}", inout_h_path.display()));
 
-    // Detect whether header is legacy (4.0) or modern (4.1+) format.
-    let is_header_4_0 = !c.contains("GDExtensionInterfaceGetProcAddress");
-    println!("is_header_4_0={is_header_4_0}");
-
-    // Sanity check
-    if let Some(is_engine_4_0) = is_engine_4_0 {
-        assert_eq!(
-            is_header_4_0, is_engine_4_0,
-            "Mismatch between engine/header versions"
-        );
-    }
-
-    if is_header_4_0 {
-        polyfill_legacy_header(&mut c);
-    }
+    // Detect whether header is legacy (4.0) format. This should generally already be checked outside.
+    assert!(
+        c.contains("GDExtensionInterfaceGetProcAddress"),
+        "C header file '{}' seems to be GDExtension version 4.0, which is no longer support by godot-rust.",
+        inout_h_path.display()
+    );
 
-    // Patch for variant converters and type constructors
+    // Patch for variant converters and type constructors.
     c = c.replace(
         "typedef void (*GDExtensionVariantFromTypeConstructorFunc)(GDExtensionVariantPtr, GDExtensionTypePtr);",
         "typedef void (*GDExtensionVariantFromTypeConstructorFunc)(GDExtensionUninitializedVariantPtr, GDExtensionTypePtr);"
@@ -217,47 +209,6 @@ fn patch_c_header(inout_h_path: &Path, is_engine_4_0: Option<bool>) {
     });
 }
 
-/// Backport Godot 4.1+ changes to the old GDExtension API, so gdext can use both uniformly.
-fn polyfill_legacy_header(c: &mut String) {
-    // Newer Uninitialized* types -- use same types as initialized ones, because old functions are not written with Uninitialized* in mind
-    let pos = c
-        .find("typedef int64_t GDExtensionInt;")
-        .expect("Unexpected gdextension_interface.h format (int)");
-
-    c.insert_str(
-        pos,
-        "\
-            // gdext polyfill\n\
-            typedef struct __GdextVariant *GDExtensionUninitializedVariantPtr;\n\
-            typedef struct __GdextStringName *GDExtensionUninitializedStringNamePtr;\n\
-            typedef struct __GdextString *GDExtensionUninitializedStringPtr;\n\
-            typedef struct __GdextObject *GDExtensionUninitializedObjectPtr;\n\
-            typedef struct __GdextType *GDExtensionUninitializedTypePtr;\n\
-            \n",
-    );
-
-    // Typedef GDExtensionInterfaceGetProcAddress (simply resolving to GDExtensionInterface, as it's the same parameter)
-    let pos = c
-        .find("/* INITIALIZATION */")
-        .expect("Unexpected gdextension_interface.h format (struct)");
-
-    c.insert_str(
-        pos,
-        "\
-            // gdext polyfill\n\
-            typedef struct {\n\
-                uint32_t major;\n\
-                uint32_t minor;\n\
-                uint32_t patch;\n\
-                const char *string;\n\
-            } GDExtensionGodotVersion;\n\
-            typedef void (*GDExtensionInterfaceFunctionPtr)();\n\
-            typedef void (*GDExtensionInterfaceGetGodotVersion)(GDExtensionGodotVersion *r_godot_version);\n\
-            typedef GDExtensionInterfaceFunctionPtr (*GDExtensionInterfaceGetProcAddress)(const char *p_function_name);\n\
-            \n",
-    );
-}
-
 pub(crate) fn locate_godot_binary() -> PathBuf {
     if let Ok(string) = std::env::var("GODOT4_BIN") {
         println!("Found GODOT4_BIN with path to executable: '{string}'");