diff --git a/packages/compiler/src/ml_parser/lexer.ts b/packages/compiler/src/ml_parser/lexer.ts
index 676afab409a6..6b1223650345 100644
--- a/packages/compiler/src/ml_parser/lexer.ts
+++ b/packages/compiler/src/ml_parser/lexer.ts
@@ -241,6 +241,8 @@ class _Tokenizer {
             }
           } else if (this._attemptCharCode(chars.$SLASH)) {
             this._consumeTagClose(start);
+          } else if (this._attemptCharCode(chars.$QUESTION)) {
+            this._consumeProcessingInstruction(start);
           } else {
             this._consumeTagOpen(start);
           }
@@ -470,30 +472,7 @@ class _Tokenizer {
   private _consumeLetDeclarationValue(): void {
     const start = this._cursor.clone();
     this._beginToken(TokenType.LET_VALUE, start);
-
-    while (this._cursor.peek() !== chars.$EOF) {
-      const char = this._cursor.peek();
-
-      // `@let` declarations terminate with a semicolon.
-      if (char === chars.$SEMICOLON) {
-        break;
-      }
-
-      // If we hit a quote, skip over its content since we don't care what's inside.
-      if (chars.isQuote(char)) {
-        this._cursor.advance();
-        this._attemptCharCodeUntilFn((inner) => {
-          if (inner === chars.$BACKSLASH) {
-            this._cursor.advance();
-            return false;
-          }
-          return inner === char;
-        });
-      }
-
-      this._cursor.advance();
-    }
-
+    this._attemptUntilCharIgnoreQuotes(chars.$SEMICOLON); // `@let` declarations terminate with a semicolon.
     this._endToken([this._cursor.getChars(start)]);
   }
 
@@ -665,6 +644,29 @@ class _Tokenizer {
     }
   }
 
+  private _attemptUntilCharIgnoreQuotes(endChar: number) {
+    while (this._cursor.peek() !== chars.$EOF) {
+      const char = this._cursor.peek();
+
+      if (char === endChar) {
+        break;
+      }
+
+      if (chars.isQuote(char)) {
+        this._cursor.advance();
+        this._attemptCharCodeUntilFn((inner) => {
+          if (inner === chars.$BACKSLASH) {
+            this._cursor.advance();
+            return false;
+          }
+          return inner === char;
+        });
+      }
+
+      this._cursor.advance();
+    }
+  }
+
   private _readChar(): string {
     // Don't rely upon reading directly from `_input` as the actual char value
     // may have been generated from an escape sequence.
@@ -800,6 +802,16 @@ class _Tokenizer {
     this._endToken([content]);
   }
 
+  private _consumeProcessingInstruction(start: CharacterCursor) {
+    this._beginToken(TokenType.PROCESSING_INSTRUCTION, start);
+    const contentStart = this._cursor.clone();
+    this._attemptUntilCharIgnoreQuotes(chars.$QUESTION);
+    const content = this._cursor.getChars(contentStart);
+    this._cursor.advance();
+    this._requireCharCode(chars.$GT);
+    this._endToken([content]);
+  }
+
   private _consumePrefixAndName(endPredicate: (code: number) => boolean): string[] {
     const nameOrPrefixStart = this._cursor.clone();
     let prefix: string = '';
@@ -1426,7 +1438,8 @@ class _Tokenizer {
         (chars.$a <= code && code <= chars.$z) ||
         (chars.$A <= code && code <= chars.$Z) ||
         code === chars.$SLASH ||
-        code === chars.$BANG
+        code === chars.$BANG ||
+        code === chars.$QUESTION
       ) {
         return true;
       }
diff --git a/packages/compiler/src/ml_parser/tokens.ts b/packages/compiler/src/ml_parser/tokens.ts
index eef8e8d7aab8..c1d16faaa6bb 100644
--- a/packages/compiler/src/ml_parser/tokens.ts
+++ b/packages/compiler/src/ml_parser/tokens.ts
@@ -51,6 +51,7 @@ export const enum TokenType {
   DIRECTIVE_NAME,
   DIRECTIVE_OPEN,
   DIRECTIVE_CLOSE,
+  PROCESSING_INSTRUCTION,
   EOF,
 }
 
@@ -95,7 +96,8 @@ export type Token =
   | IncompleteComponentOpenToken
   | DirectiveNameToken
   | DirectiveOpenToken
-  | DirectiveCloseToken;
+  | DirectiveCloseToken
+  | ProcessingInstructionToken;
 
 export type InterpolatedTextToken = TextToken | InterpolationToken | EncodedEntityToken;
 
@@ -318,3 +320,8 @@ export interface DirectiveCloseToken extends TokenBase {
   type: TokenType.DIRECTIVE_CLOSE;
   parts: [];
 }
+
+export interface ProcessingInstructionToken extends TokenBase {
+  type: TokenType.PROCESSING_INSTRUCTION;
+  parts: [content: string];
+}
diff --git a/packages/compiler/test/ml_parser/html_parser_spec.ts b/packages/compiler/test/ml_parser/html_parser_spec.ts
index 6d6badd872d1..e985bb4e608c 100644
--- a/packages/compiler/test/ml_parser/html_parser_spec.ts
+++ b/packages/compiler/test/ml_parser/html_parser_spec.ts
@@ -1629,6 +1629,20 @@ describe('HtmlParser', () => {
       });
     });
 
+    describe('ignored syntax', () => {
+      it('should ignore doctype declaration', () => {
+        expect(humanizeDom(parser.parse(`<!DOCTYPE html>hello`, 'TestComp'))).toEqual([
+          [html.Text, 'hello', 0, ['hello']],
+        ]);
+      });
+
+      it('should ignore processing instruction', () => {
+        expect(
+          humanizeDom(parser.parse(`<?xml version="1.0" encoding="UTF-8"?>hello`, 'TestComp')),
+        ).toEqual([[html.Text, 'hello', 0, ['hello']]]);
+      });
+    });
+
     describe('source spans', () => {
       it('should store the location', () => {
         expect(
diff --git a/packages/compiler/test/ml_parser/lexer_spec.ts b/packages/compiler/test/ml_parser/lexer_spec.ts
index ea96d9739440..a5373e47284f 100644
--- a/packages/compiler/test/ml_parser/lexer_spec.ts
+++ b/packages/compiler/test/ml_parser/lexer_spec.ts
@@ -158,6 +158,45 @@ describe('HtmlLexer', () => {
     });
   });
 
+  describe('processing instructions', () => {
+    it('should parse a processing instruction', () => {
+      expect(tokenizeAndHumanizeParts('<?xml version="1.0" encoding="UTF-8"?>')).toEqual([
+        [TokenType.PROCESSING_INSTRUCTION, 'xml version="1.0" encoding="UTF-8"'],
+        [TokenType.EOF],
+      ]);
+    });
+
+    it('should parse a processing instruction surrounded by other content', () => {
+      expect(
+        tokenizeAndHumanizeParts('<!DOCTYPE html>\n<?xml version="1.0" encoding="UTF-8"?> hello'),
+      ).toEqual([
+        [TokenType.DOC_TYPE, 'DOCTYPE html'],
+        [TokenType.TEXT, '\n'],
+        [TokenType.PROCESSING_INSTRUCTION, 'xml version="1.0" encoding="UTF-8"'],
+        [TokenType.TEXT, ' hello'],
+        [TokenType.EOF],
+      ]);
+    });
+
+    it('should parse a processing instruction that contains question marks inside quoted content', () => {
+      expect(tokenizeAndHumanizeParts('<?xml version="?" encoding="UTF?>-8"?>')).toEqual([
+        [TokenType.PROCESSING_INSTRUCTION, 'xml version="?" encoding="UTF?>-8"'],
+        [TokenType.EOF],
+      ]);
+    });
+
+    it('should store the location of a processing instruction', () => {
+      expect(tokenizeAndHumanizeSourceSpans('<?xml version="1.0" encoding="UTF-8"?>')).toEqual([
+        [TokenType.PROCESSING_INSTRUCTION, '<?xml version="1.0" encoding="UTF-8"?>'],
+        [TokenType.EOF, ''],
+      ]);
+    });
+
+    it('should report missing end of a processing instruction', () => {
+      expect(tokenizeAndHumanizeErrors('<?')).toEqual([['Unexpected character "EOF"', '0:2']]);
+    });
+  });
+
   describe('CDATA', () => {
     it('should parse CDATA', () => {
       expect(tokenizeAndHumanizeParts('<![CDATA[t\ne\rs\r\nt]]>')).toEqual([