diff --git a/src/ir/emit_llvm.zig b/src/ir/emit_llvm.zig
index 71bf732..2354b63 100644
--- a/src/ir/emit_llvm.zig
+++ b/src/ir/emit_llvm.zig
@@ -29,6 +29,27 @@ fn isIdentByte(b: u8) bool {
     return (b >= 'a' and b <= 'z') or (b >= 'A' and b <= 'Z') or (b >= '0' and b <= '9') or b == '_';
 }
 
+/// JNI vtable slot offsets — indices into the `JNINativeInterface`
+/// function-pointer array reachable via `*env`. Stable per the JNI
+/// spec across versions; locked to the documented order in
+/// `<jni.h>`. Slot numbers here MUST match the order of fields in
+/// the C `JNINativeInterface_` struct.
+const Jni = struct {
+    const NewGlobalRef: u32 = 21;
+    const GetObjectClass: u32 = 31;
+    const GetMethodID: u32 = 33;
+    // Call<Type>Method (instance, varargs variant). Each numeric type
+    // has its own slot — distinct ABI per return type, so the JNI
+    // runtime dispatches the right arg-shuffle for each.
+    const CallObjectMethod: u32 = 34;
+    const CallBooleanMethod: u32 = 37;
+    const CallIntMethod: u32 = 49;
+    const CallLongMethod: u32 = 52;
+    const CallFloatMethod: u32 = 55;
+    const CallDoubleMethod: u32 = 58;
+    const CallVoidMethod: u32 = 61;
+};
+
 // ── LLVMEmitter ─────────────────────────────────────────────────────────
 // Emits LLVM IR from an IR Module. This is the Phase 3 replacement for
 // the AST-based codegen.
@@ -1219,8 +1240,8 @@ pub const LLVMEmitter = struct {
                 }
                 const ret_ty_id = instruction.ty;
                 const call_method_offset: u32 = switch (ret_ty_id) {
-                    .void => 61, // CallVoidMethod
-                    .s32 => 49, // CallIntMethod
+                    .void => Jni.CallVoidMethod,
+                    .s32 => Jni.CallIntMethod,
                     else => {
                         self.mapRef(c.LLVMGetUndef(self.toLLVMType(instruction.ty)));
                         return;
@@ -1258,18 +1279,18 @@ pub const LLVMEmitter = struct {
 
                     // Miss path: GetObjectClass → NewGlobalRef → GetMethodID, then store both.
                     c.LLVMPositionBuilderAtEnd(self.builder, miss_bb);
-                    const get_obj_cls = self.loadJniFn(ifs, 31, "jni.GetObjectClass");
+                    const get_obj_cls = self.loadJniFn(ifs, Jni.GetObjectClass, "jni.GetObjectClass");
                     var gocls_params = [_]c.LLVMTypeRef{ self.cached_ptr, self.cached_ptr };
                     const gocls_ty = c.LLVMFunctionType(self.cached_ptr, &gocls_params, 2, 0);
                     var gocls_args = [_]c.LLVMValueRef{ env, target };
                     const local_cls = c.LLVMBuildCall2(self.builder, gocls_ty, get_obj_cls, &gocls_args, 2, "jni.cls");
-                    const new_global_ref = self.loadJniFn(ifs, 21, "jni.NewGlobalRef");
+                    const new_global_ref = self.loadJniFn(ifs, Jni.NewGlobalRef, "jni.NewGlobalRef");
                     var ngref_params = [_]c.LLVMTypeRef{ self.cached_ptr, self.cached_ptr };
                     const ngref_ty = c.LLVMFunctionType(self.cached_ptr, &ngref_params, 2, 0);
                     var ngref_args = [_]c.LLVMValueRef{ env, local_cls };
                     const global_cls = c.LLVMBuildCall2(self.builder, ngref_ty, new_global_ref, &ngref_args, 2, "jni.global.cls");
                     _ = c.LLVMBuildStore(self.builder, global_cls, pair.cls_slot);
-                    const get_mid = self.loadJniFn(ifs, 33, "jni.GetMethodID");
+                    const get_mid = self.loadJniFn(ifs, Jni.GetMethodID, "jni.GetMethodID");
                     var gmid_params = [_]c.LLVMTypeRef{ self.cached_ptr, self.cached_ptr, self.cached_ptr, self.cached_ptr };
                     const gmid_ty = c.LLVMFunctionType(self.cached_ptr, &gmid_params, 4, 0);
                     var gmid_args = [_]c.LLVMValueRef{ env, global_cls, name_ptr, sig_ptr };
@@ -1286,12 +1307,12 @@ pub const LLVMEmitter = struct {
                     c.LLVMAddIncoming(phi, &phi_vals, &phi_blocks, 2);
                     break :blk phi;
                 } else blk: {
-                    const get_obj_cls = self.loadJniFn(ifs, 31, "jni.GetObjectClass");
+                    const get_obj_cls = self.loadJniFn(ifs, Jni.GetObjectClass, "jni.GetObjectClass");
                     var gocls_params = [_]c.LLVMTypeRef{ self.cached_ptr, self.cached_ptr };
                     const gocls_ty = c.LLVMFunctionType(self.cached_ptr, &gocls_params, 2, 0);
                     var gocls_args = [_]c.LLVMValueRef{ env, target };
                     const cls = c.LLVMBuildCall2(self.builder, gocls_ty, get_obj_cls, &gocls_args, 2, "jni.cls");
-                    const get_mid = self.loadJniFn(ifs, 33, "jni.GetMethodID");
+                    const get_mid = self.loadJniFn(ifs, Jni.GetMethodID, "jni.GetMethodID");
                     var gmid_params = [_]c.LLVMTypeRef{ self.cached_ptr, self.cached_ptr, self.cached_ptr, self.cached_ptr };
                     const gmid_ty = c.LLVMFunctionType(self.cached_ptr, &gmid_params, 4, 0);
                     var gmid_args = [_]c.LLVMValueRef{ env, cls, name_ptr, sig_ptr };