diff --git a/lib/keyword.js b/lib/keyword.js
index 53d95c69d..5ea565c38 100644
--- a/lib/keyword.js
+++ b/lib/keyword.js
@@ -43,8 +43,6 @@ var definitionSchema = {
   }
 };
 
-var validateDefinition;
-
 /**
  * Define custom keyword
  * @this  Ajv
@@ -56,7 +54,6 @@ function addKeyword(keyword, definition) {
   /* jshint validthis: true */
   /* eslint no-shadow: 0 */
   var RULES = this.RULES;
-
   if (RULES.keywords[keyword])
     throw new Error('Keyword ' + keyword + ' is already defined');
 
@@ -64,10 +61,11 @@ function addKeyword(keyword, definition) {
     throw new Error('Keyword ' + keyword + ' is not a valid identifier');
 
   if (definition) {
-    validateDefinition = validateDefinition || this.compile(definitionSchema);
+    this.validateKeyword = this.validateKeyword
+                            || this.compile(definitionSchema, true);
 
-    if (!validateDefinition(definition))
-      throw new Error('custom keyword definition is invalid: '  + this.errorsText(validateDefinition.errors));
+    if (!this.validateKeyword(definition))
+      throw new Error('custom keyword definition is invalid: '  + this.errorsText(this.validateKeyword.errors));
 
     var dataType = definition.type;
     if (Array.isArray(dataType)) {
diff --git a/spec/issues/955_removeAdditional_custom_keywords.spec.js b/spec/issues/955_removeAdditional_custom_keywords.spec.js
new file mode 100644
index 000000000..4ef949d60
--- /dev/null
+++ b/spec/issues/955_removeAdditional_custom_keywords.spec.js
@@ -0,0 +1,48 @@
+'use strict';
+
+var Ajv = require('../ajv');
+require('../chai').should();
+
+
+describe('issue #955: option removeAdditional breaks custom keywords', function() {
+  it('should support custom keywords with option removeAdditional', function() {
+    var ajv = new Ajv({removeAdditional: 'all'});
+
+    ajv.addKeyword('minTrimmedLength', {
+      type: 'string',
+      compile: function(schema) {
+        return function(str) {
+          return str.trim().length >= schema;
+        };
+      },
+      metaSchema: {type: 'integer'}
+    });
+
+    var schema = {
+      type: 'object',
+      properties: {
+        foo: {
+          type: 'string',
+          minTrimmedLength: 3
+        }
+      },
+      required: ['foo']
+    };
+
+    var validate = ajv.compile(schema);
+
+    var data = {
+      foo: '   bar   ',
+      baz: ''
+    };
+    validate(data) .should.equal(true);
+    data .should.not.have.property('baz');
+
+    data = {
+      foo: '   ba   ',
+      baz: ''
+    };
+    validate(data) .should.equal(false);
+    data .should.not.have.property('baz');
+  });
+});