diff --git a/packages/webamp-modern-2/src/maki/interpreter.tsx b/packages/webamp-modern-2/src/maki/interpreter.tsx
index a5ba23e3..a8f88c11 100644
--- a/packages/webamp-modern-2/src/maki/interpreter.tsx
+++ b/packages/webamp-modern-2/src/maki/interpreter.tsx
@@ -146,14 +146,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -170,14 +170,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -195,14 +195,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -220,14 +220,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -304,15 +304,8 @@ class Interpreter {
           }
           const obj = this.stack.pop();
           assert(
-            obj.type === "OBJECT",
-            "Tried to call a method on a primitive."
-          );
-          assert(
-            typeof obj.value === "object",
-            "Trying to call a method on a not object"
-          );
-          assert(
-            obj.value != null,
+            (obj.type === "OBJECT" && typeof obj.value) === "object" &&
+              obj.value != null,
             "Guru Meditation: Tried to call method on null object"
           );
           let value = obj.value[methodName](...methodArgs);
@@ -326,12 +319,15 @@ class Interpreter {
             // variables[1] holds global NULL value
             value = this.variables[1];
           }
-          if (returnType === "BOOL") {
+          if (returnType === "BOOLEAN") {
             assert(typeof value === "boolean", "BOOL should return a boolean");
             value = value ? 1 : 0;
           }
           if (returnType === "OBJECT") {
-            assert(typeof value === "object", "not an object");
+            assert(
+              typeof value === "object",
+              `Expected the returned value of ${klass.name}.${methodName} to be an object, but it was "${value}"`
+            );
           }
           if (this.debug) {
             console.log(`Calling method ${methodName}`);
@@ -379,7 +375,7 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to increment a non-number.");
           }
@@ -394,7 +390,7 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to decrement a non-number.");
           }
@@ -409,7 +405,7 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to increment a non-number.");
           }
@@ -423,7 +419,7 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to increment a non-number.");
           }
@@ -437,7 +433,7 @@ class Interpreter {
           const b = this.stack.pop();
           switch (a.type) {
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error(
                 `Tried to add non-numbers: ${b.type} + ${a.type}.`
@@ -451,7 +447,7 @@ class Interpreter {
           }
           switch (b.type) {
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
               throw new Error("Tried to add non-numbers.");
           }
           // TODO: Do we need to round the value if INT?
@@ -465,14 +461,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -487,14 +483,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -509,14 +505,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
               throw new Error("Tried to add non-numbers.");
           }
           // TODO: Do we need to round the value if INT?
@@ -530,14 +526,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
               throw new Error("Tried to add non-numbers.");
             // Need to coerce LHS if not int, RHS is always int (enforced by compiler)
             case "FLOAT":
@@ -573,7 +569,7 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -588,14 +584,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
@@ -614,14 +610,14 @@ class Interpreter {
           switch (a.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
           switch (b.type) {
             case "STRING":
             case "OBJECT":
-            case "BOOL":
+            case "BOOLEAN":
             case "NULL":
               throw new Error("Tried to add non-numbers.");
           }
diff --git a/packages/webamp-modern-2/src/maki/objects.ts b/packages/webamp-modern-2/src/maki/objects.ts
index adb8ba35..56e60b45 100644
--- a/packages/webamp-modern-2/src/maki/objects.ts
+++ b/packages/webamp-modern-2/src/maki/objects.ts
@@ -23,7 +23,7 @@ const objects: { [key: string]: ObjectDefinition } = {
   ...config,
 };
 
-export function getClass(id: String): ObjectDefinition {
+export function getClass(id: string): ObjectDefinition {
   return normalizedObjects[getFormattedId(id)];
 }
 
@@ -35,9 +35,8 @@ export function getReturnType(classId: string, methodName: string): DataType {
     case "DOUBLE":
     case "STRING":
     case "FLOAT":
-      return upper as any;
     case "BOOLEAN":
-      return "BOOL";
+      return upper as any;
     case "":
       return "NULL" as any;
     default:
diff --git a/packages/webamp-modern-2/src/maki/parser.ts b/packages/webamp-modern-2/src/maki/parser.ts
index 64875038..25610e0b 100644
--- a/packages/webamp-modern-2/src/maki/parser.ts
+++ b/packages/webamp-modern-2/src/maki/parser.ts
@@ -2,6 +2,7 @@ import { COMMANDS } from "./constants";
 import { DataType, Variable } from "./v";
 import MakiFile from "./MakiFile";
 import { getReturnType } from "./objects";
+import { assert } from "../utils";
 
 export type Command = {
   opcode: number;
@@ -209,9 +210,13 @@ function readVariables({ makiFile, classes }) {
       let value = null;
 
       switch (typeName) {
-        // BOOLEAN
+        // BOOL
         case PRIMITIVE_TYPES[5]:
           value = uinit1;
+          assert(
+            value === 1 || value === 0,
+            "Expected boolean value to be initialized as zero or one"
+          );
           break;
         // INT
         case PRIMITIVE_TYPES[2]:
diff --git a/packages/webamp-modern-2/src/maki/v.ts b/packages/webamp-modern-2/src/maki/v.ts
index 312992fb..f9f24287 100644
--- a/packages/webamp-modern-2/src/maki/v.ts
+++ b/packages/webamp-modern-2/src/maki/v.ts
@@ -2,8 +2,8 @@ import BaseObject from "../skin/BaseObject";
 
 export type Variable =
   | {
-      type: "BOOL";
-      value: boolean;
+      type: "BOOLEAN";
+      value: number; // 1 || 0
     }
   | {
       type: "INT" | "FLOAT" | "DOUBLE";
@@ -36,4 +36,7 @@ export const V = {
   newInt(value: number | boolean): Variable {
     return { type: "INT", value: Number(value) };
   },
+  newBool(value: boolean): Variable {
+    return { type: "BOOLEAN", value: value ? 1 : 0 };
+  },
 };
diff --git a/packages/webamp-modern-2/src/skin/Button.ts b/packages/webamp-modern-2/src/skin/Button.ts
index 2f6009b2..0bded5e6 100644
--- a/packages/webamp-modern-2/src/skin/Button.ts
+++ b/packages/webamp-modern-2/src/skin/Button.ts
@@ -1,5 +1,6 @@
 import GuiObj from "./GuiObj";
 import UI_ROOT from "../UIRoot";
+import { V } from "../maki/v";
 
 // http://wiki.winamp.com/wiki/XML_GUI_Objects#.3Cbutton.2F.3E_.26_.3Ctogglebutton.2F.3E
 export default class Button extends GuiObj {
@@ -84,9 +85,7 @@ export default class Button extends GuiObj {
 
     if (onoff !== this._active) {
       this._active = onoff;
-      UI_ROOT.vm.dispatch(this, "onactivate", [
-        { type: "BOOL", value: onoff ? 1 : 0 },
-      ]);
+      UI_ROOT.vm.dispatch(this, "onactivate", [V.newBool(onoff)]);
     }
   }