diff --git a/packages/moon/dist/moon.js b/packages/moon/dist/moon.js
index 2f940e88..1b4b4afb 100644
--- a/packages/moon/dist/moon.js
+++ b/packages/moon/dist/moon.js
@@ -107,7 +107,7 @@
 	 */
 
 	function lexError(message, input, index) {
-		var lexMessage = message + "\n\n";
+		var lexMessage = message + "\n\n"; // Show input characters surrounding the source of the error.
 
 		for (var i = Math.max(0, index - 16); i < Math.min(index + 16, input.length); i++) {
 			lexMessage += input[i];
@@ -189,6 +189,11 @@
 				// the match and captured groups.
 
 				var typeExec = typeRE.exec(input);
+
+				if ("development" === "development" && typeExec === null) {
+					lexError("Lexer expected a valid opening or closing tag.", input, i);
+				}
+
 				var typeMatch = typeExec[0];
 				var type = typeExec[1];
 				var attributesText = typeExec[2];
@@ -302,6 +307,7 @@
 
 
 	function parseErrorMessage(message) {
+		/* istanbul ignore next */
 		return "development" === "development" ? message : "";
 	}
 	/**
diff --git a/packages/moon/dist/moon.min.js b/packages/moon/dist/moon.min.js
index 05356ef6..d410b5fd 100644
--- a/packages/moon/dist/moon.min.js
+++ b/packages/moon/dist/moon.min.js
@@ -4,4 +4,4 @@
  * Released under the MIT License
  * https://kbrsh.github.io/moon
  */
-!function(e,t){"undefined"==typeof module?e.Moon=t():module.exports=t()}(this,function(){"use strict";function a(){}function u(e,t){return void 0===e?t:e}var k=/<([\w\d-_]+)([^>]*?)(\/?)>/g,O=/\s*([\w\d-_]*)(?:=(?:("[\w\d-_]*"|'[\w\d-_]*')|{([\w\d-_]*)}))?/g;function t(e){e=e.trim();for(var t=[],n=0;n<e.length;){var r=e[n];if("<"===r){var o=e[n+1];if("/"===o){var a=e.indexOf(">",n+2),u=e.slice(n+2,a);0,t.push({type:"tagClose",value:u}),n=a+1;continue}if("!"===o&&"-"===e[n+2]&&"-"===e[n+3]){var i=e.indexOf("--\x3e",n+4);0,n=i+3;continue}k.lastIndex=n;for(var l=k.exec(e),c=l[0],s=l[1],f=l[2],m=l[3],v={},p=void 0;null!==(p=O.exec(f));){var d=p[0],y=p[1],h=p[2],x=p[3];0===d.length?O.lastIndex+=1:v[y]=void 0===x?h:x}t.push({type:"tagOpen",value:s,attributes:v,closed:"/"===m}),n+=c.length}else if("{"===r){var g="";for(n+=1;n<e.length;n++){var E=e[n];if("}"===E)break;g+=E}t.push({type:"tagOpen",value:"Text",attributes:{"":g},closed:!0}),n+=1}else{for(var b="";n<e.length;n++){var w=e[n];if("<"===w||"{"===w)break;b+=w}t.push({type:"tagOpen",value:"Text",attributes:{"":'"'+b+'"'},closed:!0})}}return t}function s(e,t,n,r){this.message=e,this.start=t,this.end=n,this.next=r}function f(e,t,n){var r=n[e],o=n[t-1],a=t-e;if(0==a)return new s("",e,t);if(1==a)return"tagOpen"===r.type&&!0===r.closed?{type:r.value,attributes:r.attributes,children:[]}:new s("",e,t);if("tagOpen"!==r.type||"tagClose"!==o.type||r.value!==o.value)return new s("",e,t);var u=function e(t,n,r){var o;if(0==n-t)return[];for(var a=t+1;a<=n;a++){var u=f(t,a,r);if(u instanceof s)o=u;else{var i=e(a,n,r);if(!(i instanceof s)){for(var l=[u],c=0;c<i.length;c++)l.push(i[c]);return l}}}return new s("",t,n,o)}(e+1,t-1,n);return u instanceof s?new s("",e,t,u):{type:r.value,attributes:r.attributes,children:u}}function n(e){var t=f(0,e.length,e);return t}var ee=function(e){return"m"+e},te=function(e,t){return ee(e)+"="+t},ne=function(e){return e.expression?e.value:'"'+e.value+'"'},re=function(e,t){return"m.rc("+ee(e)+","+ee(t)+");"},oe=function(e,t,n,r,o,a){return"m.df("+e+","+ee(t)+","+n+","+ee(r)+","+ee(o)+","+ee(a)+");"},ae=function(e,t,n){return null===n?function(e,t){return"m.ac("+ee(e)+","+ee(t)+");"}(e,t):function(e,t,n){return"m.ib("+ee(e)+","+ee(t)+","+ee(n)+");"}(e,n,t)},m=function e(t,n,r,o){switch(t.type){case"If":for(var a=r.nextElement++,u=r.nextElement++,i=r.nextElement++,l=r.nextElement++,c="[",s="[",f="",m=n.children,v=m.indexOf(t);v<m.length;v++){var p=m[v];if("If"!==p.type&&"ElseIf"!==p.type&&"Else"!==p.type)break;c+=f+("Else"===p.type?"true":ne(p.attributes[0])),s+=f+"function(locals){"+ue({element:r.nextElement,nextElement:r.nextElement+1,type:"Root",attributes:[],children:p.children},u)+"}({})",f=","}return[te(u,"m.cc();")+ae(u,n.element,o)+te(l,s+"];"),te(i,c+"];")+te(a,function(e,t,n,r){return"m.di("+ee(e)+","+ee(t)+","+ee(n)+","+ee(r)+");"}(a,i,l,n.element)),ee(a)+"[2]();"];case"ElseIf":case"Else":return["","",""];case"For":for(var d=ne(t.attributes[0]),y="[",h="",x=r.nextElement++,g=r.nextElement++,E=r.nextElement++,b=r.nextElement++,w="",k="",O=0;O<d.length;O++){var $=d[O];","===$||" "===$&&"i"===d[O+1]&&"n"===d[O+2]&&" "===d[O+3]&&(O+=3)?(y+=k+'"'+w.substring(7)+'"',w="",k=","):w+=$}return y+="]",h+=w,[te(x,"m.cc();")+ae(x,n.element,o)+te(g,"function(locals){"+ue({element:r.nextElement,nextElement:r.nextElement+1,type:"Root",attributes:[],children:t.children},x)+"};")+te(E,"[];")+te(b,"[];"),oe(y,b,h,g,E,n.element),oe(y,b,"[]",g,E,n.element)];case"Text":var _=t.attributes[0],C=r.nextElement++,I=function(e,t){return"m.stc("+ee(e)+","+t+");"}(C,ne(_)),R=te(C,function(e){return"m.ctn("+e+");"}('""')),T="";return _.dynamic?T+=I:R+=I,[R+ae(C,n.element,o),T,re(C,n.element)];default:var U=t.attributes,D=t.children;if(function(e){return e[0]===e[0].toUpperCase()&&e[0]!==e[0].toLowerCase()}(t.type)){t.component=r.nextElement++;for(var q=te(t.component,"new m.c."+t.type+"();"),F="",L=!1,M=0;M<U.length;M++){var S=U[M];if("@"===S.key[0])q+=ee(t.component)+'.on("'+S.key.substring(1)+'",function($event){locals.$event=$event;'+ne(S)+";});";else{var j=ee(t.component)+"."+S.key+"="+ne(S)+";";S.dynamic?(L=!0,F+=j):q+=j}}return q+=ee(t.component)+".create("+ee(n.element)+");",L?F+=ee(t.component)+".update();":q+=ee(t.component)+".update();",[q,F,ee(t.component)+".destroy();"]}t.element=r.nextElement++;for(var z=te(t.element,function(e){return'm.ce("'+e+'");'}(t.type)),A="",B=0;B<U.length;B++){var G=U[B],H=void 0;if("@"===G.key[0]){var J=void 0,K=void 0;if("@bind"===G.key){var N=ne(G);H=ee(t.element)+".value="+N+";",J="input",K=N+"=$event.target.value;instance.update();"}else H="",J=G.key.substring(1),K="locals.$event=$event;"+ne(G)+";";z+=(X=t.element,Y=J,Z="function($event){"+K+"}","m.ael("+ee(X)+',"'+Y+'",'+Z+");")}else V=t.element,W=G,H="m.sa("+ee(V)+',"'+W.key+'",'+ne(W)+");";G.dynamic?A+=H:z+=H}for(var P=0;P<D.length;P++){var Q=e(D[P],t,r,null);z+=Q[0],A+=Q[1]}return[z+ae(t.element,n.element,o),A,re(t.element,n.element)]}var V,W,X,Y,Z},ue=function(e,t){for(var n=e.children,r="",o="",a="",u=0;u<n.length;u++){var i=m(n[u],e,e,t);r+=i[0],o+=i[1],a+=i[2]}for(var l="var "+ee(e.element),c=e.element+1;c<e.nextElement;c++)l+=","+ee(c);return l+";return [function(_0){"+te(e.element,"_0;")+r+"},function(){"+o+"},function(){"+a+"}];"};function i(e){return n(t(e))}function e(e){function t(){}(t.prototype=e).name=u(e.name,"Root");var n=e.view;"string"==typeof n&&(n=i(n)),e.view=n,e.onCreate=u(e.onCreate,a),e.onUpdate=u(e.onUpdate,a),e.onDestroy=u(e.onDestroy,a);var r=e.root;if(delete e.root,"string"==typeof r&&(r=document.querySelector(r)),void 0===r)return t;var o=new t;return o.create(r),o}return e.lex=t,e.parse=n,e.generate=ue,e.compile=i,e});
\ No newline at end of file
+!function(e,t){"undefined"==typeof module?e.Moon=t():module.exports=t()}(this,function(){"use strict";function a(){}function u(e,t){return void 0===e?t:e}var k=/<([\w\d-_]+)([^>]*?)(\/?)>/g,O=/\s*([\w\d-_]*)(?:=(?:("[\w\d-_]*"|'[\w\d-_]*')|{([\w\d-_]*)}))?/g;function t(e){e=e.trim();for(var t=[],n=0;n<e.length;){var r=e[n];if("<"===r){var o=e[n+1];if("/"===o){var a=e.indexOf(">",n+2),u=e.slice(n+2,a);0,t.push({type:"tagClose",value:u}),n=a+1;continue}if("!"===o&&"-"===e[n+2]&&"-"===e[n+3]){var i=e.indexOf("--\x3e",n+4);0,n=i+3;continue}k.lastIndex=n;var l=k.exec(e);0;for(var c=l[0],s=l[1],f=l[2],m=l[3],v={},p=void 0;null!==(p=O.exec(f));){var d=p[0],y=p[1],h=p[2],x=p[3];0===d.length?O.lastIndex+=1:v[y]=void 0===x?h:x}t.push({type:"tagOpen",value:s,attributes:v,closed:"/"===m}),n+=c.length}else if("{"===r){var g="";for(n+=1;n<e.length;n++){var E=e[n];if("}"===E)break;g+=E}t.push({type:"tagOpen",value:"Text",attributes:{"":g},closed:!0}),n+=1}else{for(var b="";n<e.length;n++){var w=e[n];if("<"===w||"{"===w)break;b+=w}t.push({type:"tagOpen",value:"Text",attributes:{"":'"'+b+'"'},closed:!0})}}return t}function s(e,t,n,r){this.message=e,this.start=t,this.end=n,this.next=r}function f(e,t,n){var r=n[e],o=n[t-1],a=t-e;if(0==a)return new s("",e,t);if(1==a)return"tagOpen"===r.type&&!0===r.closed?{type:r.value,attributes:r.attributes,children:[]}:new s("",e,t);if("tagOpen"!==r.type||"tagClose"!==o.type||r.value!==o.value)return new s("",e,t);var u=function e(t,n,r){var o;if(0==n-t)return[];for(var a=t+1;a<=n;a++){var u=f(t,a,r);if(u instanceof s)o=u;else{var i=e(a,n,r);if(!(i instanceof s)){for(var l=[u],c=0;c<i.length;c++)l.push(i[c]);return l}}}return new s("",t,n,o)}(e+1,t-1,n);return u instanceof s?new s("",e,t,u):{type:r.value,attributes:r.attributes,children:u}}function n(e){var t=f(0,e.length,e);return t}var ee=function(e){return"m"+e},te=function(e,t){return ee(e)+"="+t},ne=function(e){return e.expression?e.value:'"'+e.value+'"'},re=function(e,t){return"m.rc("+ee(e)+","+ee(t)+");"},oe=function(e,t,n,r,o,a){return"m.df("+e+","+ee(t)+","+n+","+ee(r)+","+ee(o)+","+ee(a)+");"},ae=function(e,t,n){return null===n?function(e,t){return"m.ac("+ee(e)+","+ee(t)+");"}(e,t):function(e,t,n){return"m.ib("+ee(e)+","+ee(t)+","+ee(n)+");"}(e,n,t)},m=function e(t,n,r,o){switch(t.type){case"If":for(var a=r.nextElement++,u=r.nextElement++,i=r.nextElement++,l=r.nextElement++,c="[",s="[",f="",m=n.children,v=m.indexOf(t);v<m.length;v++){var p=m[v];if("If"!==p.type&&"ElseIf"!==p.type&&"Else"!==p.type)break;c+=f+("Else"===p.type?"true":ne(p.attributes[0])),s+=f+"function(locals){"+ue({element:r.nextElement,nextElement:r.nextElement+1,type:"Root",attributes:[],children:p.children},u)+"}({})",f=","}return[te(u,"m.cc();")+ae(u,n.element,o)+te(l,s+"];"),te(i,c+"];")+te(a,function(e,t,n,r){return"m.di("+ee(e)+","+ee(t)+","+ee(n)+","+ee(r)+");"}(a,i,l,n.element)),ee(a)+"[2]();"];case"ElseIf":case"Else":return["","",""];case"For":for(var d=ne(t.attributes[0]),y="[",h="",x=r.nextElement++,g=r.nextElement++,E=r.nextElement++,b=r.nextElement++,w="",k="",O=0;O<d.length;O++){var $=d[O];","===$||" "===$&&"i"===d[O+1]&&"n"===d[O+2]&&" "===d[O+3]&&(O+=3)?(y+=k+'"'+w.substring(7)+'"',w="",k=","):w+=$}return y+="]",h+=w,[te(x,"m.cc();")+ae(x,n.element,o)+te(g,"function(locals){"+ue({element:r.nextElement,nextElement:r.nextElement+1,type:"Root",attributes:[],children:t.children},x)+"};")+te(E,"[];")+te(b,"[];"),oe(y,b,h,g,E,n.element),oe(y,b,"[]",g,E,n.element)];case"Text":var _=t.attributes[0],C=r.nextElement++,I=function(e,t){return"m.stc("+ee(e)+","+t+");"}(C,ne(_)),R=te(C,function(e){return"m.ctn("+e+");"}('""')),T="";return _.dynamic?T+=I:R+=I,[R+ae(C,n.element,o),T,re(C,n.element)];default:var U=t.attributes,D=t.children;if(function(e){return e[0]===e[0].toUpperCase()&&e[0]!==e[0].toLowerCase()}(t.type)){t.component=r.nextElement++;for(var q=te(t.component,"new m.c."+t.type+"();"),F="",L=!1,M=0;M<U.length;M++){var S=U[M];if("@"===S.key[0])q+=ee(t.component)+'.on("'+S.key.substring(1)+'",function($event){locals.$event=$event;'+ne(S)+";});";else{var j=ee(t.component)+"."+S.key+"="+ne(S)+";";S.dynamic?(L=!0,F+=j):q+=j}}return q+=ee(t.component)+".create("+ee(n.element)+");",L?F+=ee(t.component)+".update();":q+=ee(t.component)+".update();",[q,F,ee(t.component)+".destroy();"]}t.element=r.nextElement++;for(var z=te(t.element,function(e){return'm.ce("'+e+'");'}(t.type)),A="",B=0;B<U.length;B++){var G=U[B],H=void 0;if("@"===G.key[0]){var J=void 0,K=void 0;if("@bind"===G.key){var N=ne(G);H=ee(t.element)+".value="+N+";",J="input",K=N+"=$event.target.value;instance.update();"}else H="",J=G.key.substring(1),K="locals.$event=$event;"+ne(G)+";";z+=(X=t.element,Y=J,Z="function($event){"+K+"}","m.ael("+ee(X)+',"'+Y+'",'+Z+");")}else V=t.element,W=G,H="m.sa("+ee(V)+',"'+W.key+'",'+ne(W)+");";G.dynamic?A+=H:z+=H}for(var P=0;P<D.length;P++){var Q=e(D[P],t,r,null);z+=Q[0],A+=Q[1]}return[z+ae(t.element,n.element,o),A,re(t.element,n.element)]}var V,W,X,Y,Z},ue=function(e,t){for(var n=e.children,r="",o="",a="",u=0;u<n.length;u++){var i=m(n[u],e,e,t);r+=i[0],o+=i[1],a+=i[2]}for(var l="var "+ee(e.element),c=e.element+1;c<e.nextElement;c++)l+=","+ee(c);return l+";return [function(_0){"+te(e.element,"_0;")+r+"},function(){"+o+"},function(){"+a+"}];"};function i(e){return n(t(e))}function e(e){function t(){}(t.prototype=e).name=u(e.name,"Root");var n=e.view;"string"==typeof n&&(n=i(n)),e.view=n,e.onCreate=u(e.onCreate,a),e.onUpdate=u(e.onUpdate,a),e.onDestroy=u(e.onDestroy,a);var r=e.root;if(delete e.root,"string"==typeof r&&(r=document.querySelector(r)),void 0===r)return t;var o=new t;return o.create(r),o}return e.lex=t,e.parse=n,e.generate=ue,e.compile=i,e});
\ No newline at end of file
diff --git a/packages/moon/src/compiler/lexer/lexer.js b/packages/moon/src/compiler/lexer/lexer.js
index a4a03cce..afdc679e 100644
--- a/packages/moon/src/compiler/lexer/lexer.js
+++ b/packages/moon/src/compiler/lexer/lexer.js
@@ -62,6 +62,7 @@ export function tokenString(token) {
 function lexError(message, input, index) {
 	let lexMessage = `${message}\n\n`;
 
+	// Show input characters surrounding the source of the error.
 	for (
 		let i = Math.max(0, index - 16);
 		i < Math.min(index + 16, input.length);
@@ -152,6 +153,11 @@ export function lex(input) {
 			// Execute the tag type regular expression on the input and store
 			// the match and captured groups.
 			const typeExec = typeRE.exec(input);
+
+			if (process.env.MOON_ENV === "development" && typeExec === null) {
+				lexError("Lexer expected a valid opening or closing tag.", input, i);
+			}
+
 			const typeMatch = typeExec[0];
 			const type = typeExec[1];
 			const attributesText = typeExec[2];
diff --git a/packages/moon/test/compiler/lexer.test.js b/packages/moon/test/compiler/lexer.test.js
index c0315f39..a569a424 100644
--- a/packages/moon/test/compiler/lexer.test.js
+++ b/packages/moon/test/compiler/lexer.test.js
@@ -93,6 +93,20 @@ test("lex error from unclosed opening bracket", () => {
 	expect(console.error).toBeCalled();
 });
 
+test("lex error from invalid opening tag", () => {
+	console.error = jest.fn();
+
+	expect(Array.isArray(lex("<div"))).toBe(true);
+	expect(console.error).toBeCalled();
+});
+
+test("lex error from invalid closing tag", () => {
+	console.error = jest.fn();
+
+	expect(Array.isArray(lex("<div/"))).toBe(true);
+	expect(console.error).toBeCalled();
+});
+
 test("lex error from unclosed self-closing tag", () => {
 	console.error = jest.fn();