diff --git a/HISTORY.md b/HISTORY.md
index 0394794100..b42974e879 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -4,6 +4,11 @@
 
 - Fix #2133: strongly improved the performance of `isPrime`, see #2139. 
   Thanks @Yaffle.
+- Fix #2150: give a clear error "Error: Undefined function ..." instead when
+  evaluating a non-existing function.
+- Fix #660: expose internal functions `FunctionNode.onUndefinedFunction(name)` 
+  and `SymbolNode.onUndefinedSymbol(name)`, allowing to override the behavior.
+  By default, an Error is thrown.
 
 
 # 2021-03-10, version 9.3.0
diff --git a/src/expression/node/FunctionNode.js b/src/expression/node/FunctionNode.js
index 5b71ef8323..13c1d7b140 100644
--- a/src/expression/node/FunctionNode.js
+++ b/src/expression/node/FunctionNode.js
@@ -87,29 +87,41 @@ export const createFunctionNode = /* #__PURE__ */ factory(name, dependencies, ({
       const fn = name in math ? getSafeProperty(math, name) : undefined
       const isRaw = (typeof fn === 'function') && (fn.rawArgs === true)
 
+      function resolveFn (scope) {
+        return name in scope
+          ? getSafeProperty(scope, name)
+          : name in math
+            ? getSafeProperty(math, name)
+            : FunctionNode.onUndefinedFunction(name)
+      }
+
       if (isRaw) {
         // pass unevaluated parameters (nodes) to the function
         // "raw" evaluation
         const rawArgs = this.args
         return function evalFunctionNode (scope, args, context) {
-          return (name in scope ? getSafeProperty(scope, name) : fn)(rawArgs, math, Object.assign({}, scope, args))
+          const fn = resolveFn(scope)
+          return fn(rawArgs, math, Object.assign({}, scope, args))
         }
       } else {
         // "regular" evaluation
         if (evalArgs.length === 1) {
           const evalArg0 = evalArgs[0]
           return function evalFunctionNode (scope, args, context) {
-            return (name in scope ? getSafeProperty(scope, name) : fn)(evalArg0(scope, args, context))
+            const fn = resolveFn(scope)
+            return fn(evalArg0(scope, args, context))
           }
         } else if (evalArgs.length === 2) {
           const evalArg0 = evalArgs[0]
           const evalArg1 = evalArgs[1]
           return function evalFunctionNode (scope, args, context) {
-            return (name in scope ? getSafeProperty(scope, name) : fn)(evalArg0(scope, args, context), evalArg1(scope, args, context))
+            const fn = resolveFn(scope)
+            return fn(evalArg0(scope, args, context), evalArg1(scope, args, context))
           }
         } else {
           return function evalFunctionNode (scope, args, context) {
-            return (name in scope ? getSafeProperty(scope, name) : fn).apply(null, map(evalArgs, function (evalArg) {
+            const fn = resolveFn(scope)
+            return fn.apply(null, map(evalArgs, function (evalArg) {
               return evalArg(scope, args, context)
             }))
           }
@@ -187,6 +199,14 @@ export const createFunctionNode = /* #__PURE__ */ factory(name, dependencies, ({
     return new FunctionNode(this.fn, this.args.slice(0))
   }
 
+  /**
+   * Throws an error 'Undefined function {name}'
+   * @param {string} name
+   */
+  FunctionNode.onUndefinedFunction = function (name) {
+    throw new Error('Undefined function ' + name)
+  }
+
   // backup Node's toString function
   // @private
   const nodeToString = FunctionNode.prototype.toString
diff --git a/src/expression/node/SymbolNode.js b/src/expression/node/SymbolNode.js
index b3cc888641..ffcdab3f08 100644
--- a/src/expression/node/SymbolNode.js
+++ b/src/expression/node/SymbolNode.js
@@ -80,7 +80,7 @@ export const createSymbolNode = /* #__PURE__ */ factory(name, dependencies, ({ m
           ? getSafeProperty(scope, name)
           : isUnit
             ? new Unit(null, name)
-            : undef(name)
+            : SymbolNode.onUndefinedSymbol(name)
       }
     }
   }
@@ -107,7 +107,7 @@ export const createSymbolNode = /* #__PURE__ */ factory(name, dependencies, ({ m
    * Throws an error 'Undefined symbol {name}'
    * @param {string} name
    */
-  function undef (name) {
+  SymbolNode.onUndefinedSymbol = function (name) {
     throw new Error('Undefined symbol ' + name)
   }
 
diff --git a/test/unit-tests/expression/node/FunctionNode.test.js b/test/unit-tests/expression/node/FunctionNode.test.js
index a10ad970a9..a26c5bcfc7 100644
--- a/test/unit-tests/expression/node/FunctionNode.test.js
+++ b/test/unit-tests/expression/node/FunctionNode.test.js
@@ -53,6 +53,12 @@ describe('FunctionNode', function () {
     assert.strictEqual(n3.name, '')
   })
 
+  it('should throw an error when evaluating an undefined function', function () {
+    const scope = {}
+    const s = new FunctionNode('foo', [])
+    assert.throws(function () { s.compile().evaluate(scope) }, /Error: Undefined function foo/)
+  })
+
   it('should compile a FunctionNode', function () {
     const s = new SymbolNode('sqrt')
     const c = new ConstantNode(4)
diff --git a/test/unit-tests/expression/node/SymbolNode.test.js b/test/unit-tests/expression/node/SymbolNode.test.js
index cebea67c73..b26856c9a7 100644
--- a/test/unit-tests/expression/node/SymbolNode.test.js
+++ b/test/unit-tests/expression/node/SymbolNode.test.js
@@ -32,7 +32,7 @@ describe('SymbolNode', function () {
   it('should throw an error when evaluating an undefined symbol', function () {
     const scope = {}
     const s = new SymbolNode('foo')
-    assert.throws(function () { s.compile().evaluate(scope) }, Error)
+    assert.throws(function () { s.compile().evaluate(scope) }, /Error: Undefined symbol foo/)
   })
 
   it('should compile a SymbolNode', function () {
diff --git a/test/unit-tests/expression/security.test.js b/test/unit-tests/expression/security.test.js
index c8ca826a47..720ffa0e21 100644
--- a/test/unit-tests/expression/security.test.js
+++ b/test/unit-tests/expression/security.test.js
@@ -104,7 +104,7 @@ describe('security', function () {
     assert.throws(function () {
       const math2 = math.create()
       math2.evaluate('import({matrix:cos.constructor},{override:1});x=["console.log(\'hacked...\')"];x()')
-    }, /Error: No access to property "constructor"/)
+    }, /Error: Undefined function import/)
   })
 
   it('should not allow calling Function via index retrieval', function () {
@@ -297,13 +297,13 @@ describe('security', function () {
       math.evaluate('f=chain("a(){return evaluate;};function b").typed({"":f()=0}).done();' +
           'g=f();' +
           "g(\"console.log('hacked...')\")")
-    }, /(is not a function)|(Object expected)/)
+    }, /Error: Undefined function chain/)
   })
 
   it('should not allow using method chain (2)', function () {
     assert.throws(function () {
       math.evaluate("evilMath=chain().create().done();evilMath.import({\"_compile\":f(a,b,c)=\"evaluate\",\"isNode\":f()=true}); parse(\"(1)\").map(g(a,b,c)=evilMath.chain()).compile().evaluate()(\"console.log('hacked...')\")")
-    }, /(Cannot read property 'apply' of undefined)|(undefined has no properties)|(undefined is not an object)|(Unable to get property 'apply' of undefined or null reference)/)
+    }, /Error: Undefined function chain/)
   })
 
   it('should not allow using method Chain', function () {