diff --git a/components/prism-crystal.js b/components/prism-crystal.js
index 47554147a9..66f24fb302 100644
--- a/components/prism-crystal.js
+++ b/components/prism-crystal.js
@@ -1,7 +1,7 @@
 (function(Prism) {
 	Prism.languages.crystal = Prism.languages.extend('ruby', {
 		keyword: [
-			/\b(?:abstract|alias|as|asm|begin|break|case|class|def|do|else|elsif|end|ensure|enum|extend|for|fun|if|ifdef|include|instance_sizeof|lib|macro|module|next|of|out|pointerof|private|protected|rescue|return|require|self|sizeof|struct|super|then|type|typeof|undef|union|unless|until|when|while|with|yield|__DIR__|__FILE__|__LINE__)\b/,
+			/\b(?:abstract|alias|as|asm|begin|break|case|class|def|do|else|elsif|end|ensure|enum|extend|for|fun|if|ifdef|include|instance_sizeof|lib|macro|module|next|of|out|pointerof|private|protected|rescue|return|require|self|sizeof|struct|super|then|type|typeof|union|unless|until|when|while|with|yield|__DIR__|__FILE__|__LINE__)\b/,
 			{
 				pattern: /(\.\s*)(?:is_a|responds_to)\?/,
 				lookbehind: true
diff --git a/tests/languages/crystal/keyword_feature.test b/tests/languages/crystal/keyword_feature.test
index 2d58f50a25..ca575efb2a 100644
--- a/tests/languages/crystal/keyword_feature.test
+++ b/tests/languages/crystal/keyword_feature.test
@@ -8,7 +8,7 @@ lib macro module next of out pointerof
 private protected rescue
 .responds_to?
 return require self sizeof struct super
-then type typeof undef union unless until when
+then type typeof union unless until when
 while with yield __DIR__ __FILE__ __LINE__
 
 ----------------------------------------------------
@@ -24,7 +24,7 @@ while with yield __DIR__ __FILE__ __LINE__
 	["keyword", "private"], ["keyword", "protected"], ["keyword", "rescue"],
 	["punctuation", "."], ["keyword", "responds_to?"],
 	["keyword", "return"], ["keyword", "require"], ["keyword", "self"], ["keyword", "sizeof"], ["keyword", "struct"], ["keyword", "super"],
-	["keyword", "then"], ["keyword", "type"], ["keyword", "typeof"], ["keyword", "undef"], ["keyword", "union"], ["keyword", "unless"], ["keyword", "until"], ["keyword", "when"],
+	["keyword", "then"], ["keyword", "type"], ["keyword", "typeof"], ["keyword", "union"], ["keyword", "unless"], ["keyword", "until"], ["keyword", "when"],
 	["keyword", "while"], ["keyword", "with"], ["keyword", "yield"], ["keyword", "__DIR__"], ["keyword", "__FILE__"], ["keyword", "__LINE__"]
 ]