diff --git a/src/codegen/types/objects/regex.ts b/src/codegen/types/objects/regex.ts
index 6fb18533..99178419 100644
--- a/src/codegen/types/objects/regex.ts
+++ b/src/codegen/types/objects/regex.ts
@@ -50,15 +50,66 @@ export class RegexGenerator {
     return hi + lo;
   }
 
-  // Compile a regex pattern and return a pointer to the compiled regex
-  // Returns a pointer to regex_t struct (i8*)
+  private translateJSPatternToPOSIX(pattern: string): string {
+    let result = "";
+    let inBracket = false;
+    for (let i = 0; i < pattern.length; i++) {
+      const ch = pattern[i];
+      if (ch === "\\" && i + 1 < pattern.length) {
+        const next = pattern[i + 1];
+        if (next === "d") {
+          result += inBracket ? "0-9" : "[0-9]";
+          i++;
+          continue;
+        }
+        if (next === "D") {
+          result += inBracket ? "^0-9" : "[^0-9]";
+          i++;
+          continue;
+        }
+        if (next === "w") {
+          result += inBracket ? "a-zA-Z0-9_" : "[a-zA-Z0-9_]";
+          i++;
+          continue;
+        }
+        if (next === "W") {
+          result += inBracket ? "^a-zA-Z0-9_" : "[^a-zA-Z0-9_]";
+          i++;
+          continue;
+        }
+        if (next === "s") {
+          result += inBracket ? " \\t\\n\\r" : "[ \\t\\n\\r]";
+          i++;
+          continue;
+        }
+        if (next === "S") {
+          result += inBracket ? "^ \\t\\n\\r" : "[^ \\t\\n\\r]";
+          i++;
+          continue;
+        }
+        result += ch;
+        result += next;
+        i++;
+        continue;
+      }
+      if (ch === "[" && !inBracket) {
+        inBracket = true;
+      } else if (ch === "]" && inBracket) {
+        inBracket = false;
+      }
+      result += ch;
+    }
+    return result;
+  }
+
   generateRegexCompile(pattern: string, flags: string): string {
     this.ctx.setUsesRegex(true);
+    const posixPattern = this.translateJSPatternToPOSIX(pattern);
     let escaped = "";
     let byteCount = 0;
-    for (let i = 0; i < pattern.length; i++) {
-      const ch = pattern[i];
-      const code = pattern.charCodeAt(i);
+    for (let i = 0; i < posixPattern.length; i++) {
+      const ch = posixPattern[i];
+      const code = posixPattern.charCodeAt(i);
       if (ch === "\\") {
         escaped += "\\5C";
         byteCount += 1;
diff --git a/tests/fixtures/regex/regex-character-classes.ts b/tests/fixtures/regex/regex-character-classes.ts
new file mode 100644
index 00000000..92ca34c9
--- /dev/null
+++ b/tests/fixtures/regex/regex-character-classes.ts
@@ -0,0 +1,64 @@
+function testCharacterClasses(): void {
+  const str = "hello 123 world";
+
+  const digitMatch = str.match(/(\d+)/);
+  if (digitMatch === null) {
+    console.log("FAIL: \\d should match digits");
+    process.exit(1);
+  }
+  if (digitMatch[0] !== "123") {
+    console.log("FAIL: \\d match[0] expected 123, got " + digitMatch[0]);
+    process.exit(1);
+  }
+
+  const wordMatch = str.match(/(\w+)/);
+  if (wordMatch === null) {
+    console.log("FAIL: \\w should match word chars");
+    process.exit(1);
+  }
+  if (wordMatch[0] !== "hello") {
+    console.log("FAIL: \\w match[0] expected hello, got " + wordMatch[0]);
+    process.exit(1);
+  }
+
+  const spaceMatch = str.match(/(\s+)/);
+  if (spaceMatch === null) {
+    console.log("FAIL: \\s should match whitespace");
+    process.exit(1);
+  }
+  if (spaceMatch[0] !== " ") {
+    console.log("FAIL: \\s match[0] expected space, got '" + spaceMatch[0] + "'");
+    process.exit(1);
+  }
+
+  const nonDigitMatch = str.match(/(\D+)/);
+  if (nonDigitMatch === null || nonDigitMatch[0] !== "hello ") {
+    console.log("FAIL: \\D should match non-digits");
+    process.exit(1);
+  }
+
+  const nonWordMatch = str.match(/(\W+)/);
+  if (nonWordMatch === null || nonWordMatch[0] !== " ") {
+    console.log("FAIL: \\W should match non-word chars");
+    process.exit(1);
+  }
+
+  const nonSpaceMatch = str.match(/(\S+)/);
+  if (nonSpaceMatch === null || nonSpaceMatch[0] !== "hello") {
+    console.log("FAIL: \\S should match non-space");
+    process.exit(1);
+  }
+
+  if (!/\d{3}-\d{4}/.test("555-1234")) {
+    console.log("FAIL: phone pattern should match");
+    process.exit(1);
+  }
+
+  if (/\d+/.test("no digits here")) {
+    console.log("FAIL: \\d should not match letters");
+    process.exit(1);
+  }
+
+  console.log("TEST_PASSED");
+}
+testCharacterClasses();