diff --git a/.changeset/funny-pens-peel.md b/.changeset/funny-pens-peel.md
new file mode 100644
index 00000000..2116b2a1
--- /dev/null
+++ b/.changeset/funny-pens-peel.md
@@ -0,0 +1,5 @@
+---
+"htmljs-parser": patch
+---
+
+Fix regexp charset parsing issue.
diff --git a/src/__tests__/fixtures/attr-regex-character-classes/__snapshots__/attr-regex-character-classes.expected.txt b/src/__tests__/fixtures/attr-regex-character-classes/__snapshots__/attr-regex-character-classes.expected.txt
new file mode 100644
index 00000000..24288051
--- /dev/null
+++ b/src/__tests__/fixtures/attr-regex-character-classes/__snapshots__/attr-regex-character-classes.expected.txt
@@ -0,0 +1,51 @@
+1╭─ <div pattern=/[abc/] /></div>
+ │  ││   │      ││        ││ │  ╰─ closeTagEnd(div)
+ │  ││   │      ││        ││ ╰─ closeTagName "div"
+ │  ││   │      ││        │╰─ closeTagStart "</"
+ │  ││   │      ││        ╰─ openTagEnd
+ │  ││   │      │╰─ attrValue.value "/[abc/] /"
+ │  ││   │      ╰─ attrValue "=/[abc/] /"
+ │  ││   ╰─ attrName "pattern"
+ │  │╰─ tagName "div"
+ ╰─ ╰─ openTagStart
+2╭─ <div pattern=/[a-z/] /></div>
+ │  ││   │      ││        ││ │  ╰─ closeTagEnd(div)
+ │  ││   │      ││        ││ ╰─ closeTagName "div"
+ │  ││   │      ││        │╰─ closeTagStart "</"
+ │  ││   │      ││        ╰─ openTagEnd
+ │  ││   │      │╰─ attrValue.value "/[a-z/] /"
+ │  ││   │      ╰─ attrValue "=/[a-z/] /"
+ │  ││   ╰─ attrName "pattern"
+ │  │╰─ tagName "div"
+ ╰─ ╰─ openTagStart
+3╭─ <div pattern=/[^abc/] /></div>
+ │  ││   │      ││         ││ │  ╰─ closeTagEnd(div)
+ │  ││   │      ││         ││ ╰─ closeTagName "div"
+ │  ││   │      ││         │╰─ closeTagStart "</"
+ │  ││   │      ││         ╰─ openTagEnd
+ │  ││   │      │╰─ attrValue.value "/[^abc/] /"
+ │  ││   │      ╰─ attrValue "=/[^abc/] /"
+ │  ││   ╰─ attrName "pattern"
+ │  │╰─ tagName "div"
+ ╰─ ╰─ openTagStart
+4╭─ <div pattern=/[a\]b/] /></div>
+ │  ││   │      ││         ││ │  ╰─ closeTagEnd(div)
+ │  ││   │      ││         ││ ╰─ closeTagName "div"
+ │  ││   │      ││         │╰─ closeTagStart "</"
+ │  ││   │      ││         ╰─ openTagEnd
+ │  ││   │      │╰─ attrValue.value "/[a\\]b/] /"
+ │  ││   │      ╰─ attrValue "=/[a\\]b/] /"
+ │  ││   ╰─ attrName "pattern"
+ │  │╰─ tagName "div"
+ ╰─ ╰─ openTagStart
+5╭─ <div pattern=/[\w\s/] /></div>
+ │  ││   │      ││         ││ │  ╰─ closeTagEnd(div)
+ │  ││   │      ││         ││ ╰─ closeTagName "div"
+ │  ││   │      ││         │╰─ closeTagStart "</"
+ │  ││   │      ││         ╰─ openTagEnd
+ │  ││   │      │╰─ attrValue.value "/[\\w\\s/] /"
+ │  ││   │      ╰─ attrValue "=/[\\w\\s/] /"
+ │  ││   ╰─ attrName "pattern"
+ │  │╰─ tagName "div"
+ ╰─ ╰─ openTagStart
+6╰─ 
\ No newline at end of file
diff --git a/src/__tests__/fixtures/attr-regex-character-classes/input.marko b/src/__tests__/fixtures/attr-regex-character-classes/input.marko
new file mode 100644
index 00000000..e8649cd6
--- /dev/null
+++ b/src/__tests__/fixtures/attr-regex-character-classes/input.marko
@@ -0,0 +1,5 @@
+<div pattern=/[abc/] /></div>
+<div pattern=/[a-z/] /></div>
+<div pattern=/[^abc/] /></div>
+<div pattern=/[a\]b/] /></div>
+<div pattern=/[\w\s/] /></div>
diff --git a/src/states/REGULAR_EXPRESSION.ts b/src/states/REGULAR_EXPRESSION.ts
index 7afaa523..3432e301 100644
--- a/src/states/REGULAR_EXPRESSION.ts
+++ b/src/states/REGULAR_EXPRESSION.ts
@@ -18,16 +18,23 @@ export const REGULAR_EXPRESSION: StateDefinition<RegExpMeta> = {
   exit() {},
 
   char(code, regExp) {
-    if (code === CODE.BACK_SLASH) {
-      // Handle escape sequence
-      this.pos++; // skip \
-    } else if (code === CODE.OPEN_SQUARE_BRACKET && regExp.isInCharSet) {
-      regExp.isInCharSet = true;
-    } else if (code === CODE.CLOSE_SQUARE_BRACKET && regExp.isInCharSet) {
-      regExp.isInCharSet = false;
-    } else if (code === CODE.FORWARD_SLASH && !regExp.isInCharSet) {
-      this.pos++; // skip /
-      this.exitState();
+    switch (code) {
+      case CODE.BACK_SLASH:
+        // Handle escape sequence
+        this.pos++; // skip \
+        break;
+      case CODE.OPEN_SQUARE_BRACKET:
+        regExp.isInCharSet = true;
+        break;
+      case CODE.CLOSE_SQUARE_BRACKET:
+        regExp.isInCharSet = false;
+        break;
+      case CODE.FORWARD_SLASH:
+        if (!regExp.isInCharSet) {
+          this.pos++; // skip /
+          this.exitState();
+        }
+        break;
     }
   },