diff --git a/deno/lib/__tests__/string.test.ts b/deno/lib/__tests__/string.test.ts
index 3f5b95562..3fc6ec0f4 100644
--- a/deno/lib/__tests__/string.test.ts
+++ b/deno/lib/__tests__/string.test.ts
@@ -331,6 +331,8 @@ test("ulid", () => {
   if (!result.success) {
     expect(result.error.issues[0].message).toEqual("Invalid ulid");
   }
+  const caseInsensitive = ulid.safeParse("01arZ3nDeKTsV4RRffQ69G5FAV")
+  expect(caseInsensitive.success).toEqual(true)
 });
 
 test("regex", () => {
diff --git a/deno/lib/types.ts b/deno/lib/types.ts
index 9a6311289..d634e524f 100644
--- a/deno/lib/types.ts
+++ b/deno/lib/types.ts
@@ -575,7 +575,7 @@ export interface ZodStringDef extends ZodTypeDef {
 
 const cuidRegex = /^c[^\s-]{8,}$/i;
 const cuid2Regex = /^[0-9a-z]+$/;
-const ulidRegex = /^[0-9A-HJKMNP-TV-Z]{26}$/;
+const ulidRegex = /^[0-9A-HJKMNP-TV-Z]{26}$/i;
 // const uuidRegex =
 //   /^([a-f0-9]{8}-[a-f0-9]{4}-[1-5][a-f0-9]{3}-[a-f0-9]{4}-[a-f0-9]{12}|00000000-0000-0000-0000-000000000000)$/i;
 const uuidRegex =
diff --git a/src/__tests__/string.test.ts b/src/__tests__/string.test.ts
index db01a64eb..b79664fff 100644
--- a/src/__tests__/string.test.ts
+++ b/src/__tests__/string.test.ts
@@ -330,6 +330,8 @@ test("ulid", () => {
   if (!result.success) {
     expect(result.error.issues[0].message).toEqual("Invalid ulid");
   }
+  const caseInsensitive = ulid.safeParse("01arZ3nDeKTsV4RRffQ69G5FAV")
+  expect(caseInsensitive.success).toEqual(true)
 });
 
 test("regex", () => {
diff --git a/src/types.ts b/src/types.ts
index f89acb5e0..0767073c5 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -575,7 +575,7 @@ export interface ZodStringDef extends ZodTypeDef {
 
 const cuidRegex = /^c[^\s-]{8,}$/i;
 const cuid2Regex = /^[0-9a-z]+$/;
-const ulidRegex = /^[0-9A-HJKMNP-TV-Z]{26}$/;
+const ulidRegex = /^[0-9A-HJKMNP-TV-Z]{26}$/i;
 // const uuidRegex =
 //   /^([a-f0-9]{8}-[a-f0-9]{4}-[1-5][a-f0-9]{3}-[a-f0-9]{4}-[a-f0-9]{12}|00000000-0000-0000-0000-000000000000)$/i;
 const uuidRegex =