diff --git a/commonmark/src/main/java/org/commonmark/internal/HtmlBlockParser.java b/commonmark/src/main/java/org/commonmark/internal/HtmlBlockParser.java
index 6dcb6252..bcbf852f 100644
--- a/commonmark/src/main/java/org/commonmark/internal/HtmlBlockParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/HtmlBlockParser.java
@@ -34,7 +34,7 @@ public class HtmlBlockParser extends AbstractBlockParser {
                 },
                 {Pattern.compile("^<!--"), Pattern.compile("-->")},
                 {Pattern.compile("^<[?]"), Pattern.compile("\\?>")},
-                {Pattern.compile("^<![A-Z]"), Pattern.compile(">")},
+                {Pattern.compile("^<![A-Za-z]"), Pattern.compile(">")},
                 {Pattern.compile("^<!\\[CDATA\\["), Pattern.compile("\\]\\]>")},
                 {
                     Pattern.compile(
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
index babcb90f..a6560b17 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
@@ -245,9 +245,6 @@ private boolean tryDeclaration(Scanner scanner) {
             return false;
         }
         scanner.match(asciiLetter);
-        if (scanner.whitespace() <= 0) {
-            return false;
-        }
         if (scanner.find('>') >= 0) {
             scanner.next();
             return true;
diff --git a/commonmark/src/test/java/org/commonmark/test/HtmlInlineParserTest.java b/commonmark/src/test/java/org/commonmark/test/HtmlInlineParserTest.java
index 454c1de8..1cd59d77 100644
--- a/commonmark/src/test/java/org/commonmark/test/HtmlInlineParserTest.java
+++ b/commonmark/src/test/java/org/commonmark/test/HtmlInlineParserTest.java
@@ -28,7 +28,7 @@ public void afterFailedAttempt() {
         assertRendering("inline <?? <?php ?>", "<p>inline &lt;?? <?php ?></p>\n");
         assertRendering(
                 "inline <![x]]> <![CDATA[a]]>", "<p>inline &lt;![x]]&gt; <![CDATA[a]]></p>\n");
-        assertRendering("inline <!foo> <!bar baz>", "<p>inline &lt;!foo&gt; <!bar baz></p>\n");
+        assertRendering("inline <!1> <!bar baz>", "<p>inline &lt;!1&gt; <!bar baz></p>\n");
     }
 
     @Test
@@ -45,12 +45,12 @@ public void unterminatedConstructDoesNotAffectLaterParagraph() {
 
     @Test
     public void declaration() {
-        // Whitespace is mandatory
-        assertRendering("inline <!FOO>", "<p>inline &lt;!FOO&gt;</p>\n");
+        assertRendering("inline <!FOO>", "<p>inline <!FOO></p>\n");
         assertRendering("inline <!FOO >", "<p>inline <!FOO ></p>\n");
         assertRendering("inline <!FOO 'bar'>", "<p>inline <!FOO 'bar'></p>\n");
 
         // Lowercase
         assertRendering("inline <!foo bar>", "<p>inline <!foo bar></p>\n");
+        assertRendering("inline <!foo>", "<p>inline <!foo></p>\n");
     }
 }
diff --git a/commonmark/src/test/java/org/commonmark/test/SpecialInputTest.java b/commonmark/src/test/java/org/commonmark/test/SpecialInputTest.java
index 43b7686c..4e51b680 100644
--- a/commonmark/src/test/java/org/commonmark/test/SpecialInputTest.java
+++ b/commonmark/src/test/java/org/commonmark/test/SpecialInputTest.java
@@ -48,6 +48,12 @@ public void surrogatePairInLinkDestination() {
         assertRendering("[title](\uD834\uDD1E)", "<p><a href=\"\uD834\uDD1E\">title</a></p>\n");
     }
 
+    @Test
+    public void htmlBlockDeclarationWithLowercaseLetter() {
+        assertRendering("<!doctype html>", "<!doctype html>\n");
+        assertRendering("<!x\nfoo>\nbar", "<!x\nfoo>\n<p>bar</p>\n");
+    }
+
     @Test
     public void indentedCodeBlockWithMixedTabsAndSpaces() {
         assertRendering("    foo\n\tbar", "<pre><code>foo\nbar\n</code></pre>\n");