diff --git a/src/vm.ts b/src/vm.ts
index b116f7d..f451e1e 100644
--- a/src/vm.ts
+++ b/src/vm.ts
@@ -565,7 +565,7 @@ export class VM {
         }
 
         if (fn.type !== 'function')
-          throw new Error('CALL: not a function')
+          throw new Error(`CALL: ${fn.type} is not a function (${fn.value})`)
 
         if (this.callStack.length > 0)
           this.callStack[this.callStack.length - 1]!.isBreakTarget = true
@@ -657,7 +657,7 @@ export class VM {
         const tailFn = this.stack.pop()!
 
         if (tailFn.type !== 'function')
-          throw new Error('TAIL_CALL: not a function')
+          throw new Error(`TAIL_CALL: ${tailFn.type} is not a function (${tailFn.value})`)
 
         this.scope = new Scope(tailFn.parentScope)