diff --git a/mordant-baseline.toml b/mordant-baseline.toml
index ed3d11479351..41e0f42195f9 100644
--- a/mordant-baseline.toml
+++ b/mordant-baseline.toml
@@ -30,7 +30,6 @@
 "reimplemented_helper:src/react_compiler/reactive_scopes/propagate_early_returns.rs" = 1
 
 [bun_runtime]
-"bare_bool_args:src/runtime/api.rs" = 2
 "defaulted_failure:src/runtime/ffi/ffi_body.rs" = 1
 "defaulted_failure:src/runtime/server/RequestContext.rs" = 1
 "defaulted_failure:src/runtime/test_runner/pretty_format.rs" = 4
diff --git a/src/runtime/api.rs b/src/runtime/api.rs
index 680029fafff1..8e2f9ec34edc 100644
--- a/src/runtime/api.rs
+++ b/src/runtime/api.rs
@@ -218,21 +218,47 @@ fn with_text_format_source<R>(
     global: &bun_jsc::JSGlobalObject,
     frame: &bun_jsc::CallFrame,
     path: &'static [u8],
-    accept_blob_or_buffer: bool,
-    reject_nullish: bool,
+    blob_or_buffer_input: BlobOrBufferInput,
+    nullish_input: NullishInput,
     f: impl FnOnce(&bun_alloc::Arena, &mut bun_ast::Log, &bun_ast::Source) -> bun_jsc::JsResult<R>,
 ) -> bun_jsc::JsResult<R> {
     with_text_format_source_encoded(
         global,
         frame,
         path,
-        accept_blob_or_buffer,
-        reject_nullish,
-        false,
+        blob_or_buffer_input,
+        nullish_input,
+        StringInput::Utf8,
         |arena, log, source, _| f(arena, log, source),
     )
 }
 
+/// What `parse` does with a `Blob`, `ArrayBuffer`, typed array or `DataView`.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum BlobOrBufferInput {
+    /// Parses its bytes.
+    Bytes,
+    /// Stringifies it like any other argument, as `JSON.parse` would.
+    ToString,
+}
+
+/// What `parse` does with an `undefined` or `null` argument.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum NullishInput {
+    Throw,
+    /// Parses the text `"undefined"` / `"null"`.
+    ToString,
+}
+
+/// What `parse` hands the closure for a string argument.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum StringInput {
+    /// The string re-encoded as UTF-8 ([`SourceEncoding::Utf8Text`]).
+    Utf8,
+    /// The string's own storage, Latin-1 or UTF-16, as is.
+    AsIs,
+}
+
 /// How the bytes handed to the closure of
 /// [`with_text_format_source_encoded`] are encoded.
 #[derive(Clone, Copy, PartialEq, Eq)]
@@ -241,10 +267,10 @@ enum SourceEncoding {
     Bytes,
     /// A JS string, re-encoded as UTF-8.
     Utf8Text,
-    /// A Latin-1 JS string, borrowed as is (only when `string_passthrough`).
+    /// A Latin-1 JS string, borrowed as is (only under [`StringInput::AsIs`]).
     Latin1Text,
     /// A UTF-16 JS string, borrowed as is: the bytes are its code units
-    /// (only when `string_passthrough`).
+    /// (only under [`StringInput::AsIs`]).
     Utf16Text,
 }
 
@@ -252,9 +278,9 @@ fn with_text_format_source_encoded<R>(
     global: &bun_jsc::JSGlobalObject,
     frame: &bun_jsc::CallFrame,
     path: &'static [u8],
-    accept_blob_or_buffer: bool,
-    reject_nullish: bool,
-    string_passthrough: bool,
+    blob_or_buffer_input: BlobOrBufferInput,
+    nullish_input: NullishInput,
+    string_input: StringInput,
     f: impl FnOnce(
         &bun_alloc::Arena,
         &mut bun_ast::Log,
@@ -286,7 +312,7 @@ fn with_text_format_source_encoded<R>(
     let _ast_scope = ast_memory_allocator.enter();
 
     let input_value = frame.argument(0);
-    if reject_nullish && input_value.is_empty_or_undefined_or_null() {
+    if nullish_input == NullishInput::Throw && input_value.is_empty_or_undefined_or_null() {
         return Err(global.throw_invalid_arguments(format_args!("Expected a string to parse")));
     }
 
@@ -299,7 +325,7 @@ fn with_text_format_source_encoded<R>(
     let _latin1_hold: bun_core::OwnedString;
     let mut encoding = SourceEncoding::Utf8Text;
     let bytes: &[u8] = 'bytes: {
-        if accept_blob_or_buffer && !input_value.is_string() {
+        if blob_or_buffer_input == BlobOrBufferInput::Bytes && !input_value.is_string() {
             if let Some(v) = BlobOrStringOrBuffer::from_js(global, input_value)? {
                 _blob_hold = v;
                 encoding = SourceEncoding::Bytes;
@@ -307,7 +333,7 @@ fn with_text_format_source_encoded<R>(
             }
         }
         let mut s = input_value.to_bun_string(global)?;
-        if string_passthrough {
+        if string_input == StringInput::AsIs {
             _latin1_hold = bun_core::OwnedString::new(s);
             if _latin1_hold.is_8bit() {
                 encoding = SourceEncoding::Latin1Text;
diff --git a/src/runtime/api/JSON5Object.rs b/src/runtime/api/JSON5Object.rs
index 233918df8c25..0344526b0562 100644
--- a/src/runtime/api/JSON5Object.rs
+++ b/src/runtime/api/JSON5Object.rs
@@ -49,8 +49,8 @@ pub(crate) fn parse(global: &JSGlobalObject, frame: &CallFrame) -> JsResult<JSVa
         global,
         frame,
         b"input.json5",
-        true,
-        true,
+        super::BlobOrBufferInput::Bytes,
+        super::NullishInput::Throw,
         |bump, log, source| {
             let root = match json5::JSON5Parser::parse(source, log, bump) {
                 Ok(r) => r,
diff --git a/src/runtime/api/JSONCObject.rs b/src/runtime/api/JSONCObject.rs
index 5c0b8f5d9acd..19a745bfe7dc 100644
--- a/src/runtime/api/JSONCObject.rs
+++ b/src/runtime/api/JSONCObject.rs
@@ -14,8 +14,8 @@ pub(crate) fn parse(global: &JSGlobalObject, frame: &CallFrame) -> JsResult<JSVa
         global,
         frame,
         b"input.jsonc",
-        false,
-        true,
+        super::BlobOrBufferInput::ToString,
+        super::NullishInput::Throw,
         |_arena, log, source| {
             // parse_jsonc maps empty input to {}; the public API rejects it like JSON.parse.
             if source.contents.is_empty() {
diff --git a/src/runtime/api/TOMLObject.rs b/src/runtime/api/TOMLObject.rs
index 5ae7cb4409e6..313b0efca6d8 100644
--- a/src/runtime/api/TOMLObject.rs
+++ b/src/runtime/api/TOMLObject.rs
@@ -22,8 +22,8 @@ pub(crate) fn parse(global: &JSGlobalObject, frame: &CallFrame) -> JsResult<JSVa
         global,
         frame,
         b"input.toml",
-        true,
-        true,
+        super::BlobOrBufferInput::Bytes,
+        super::NullishInput::Throw,
         |arena, log, source| {
             let root = match TOML::parse(source, log, arena, false) {
                 Ok(v) => v,
diff --git a/src/runtime/api/XMLObject.rs b/src/runtime/api/XMLObject.rs
index b53543d22420..f3f9e562f6aa 100644
--- a/src/runtime/api/XMLObject.rs
+++ b/src/runtime/api/XMLObject.rs
@@ -52,9 +52,9 @@ pub(crate) fn parse(global: &JSGlobalObject, frame: &CallFrame) -> JsResult<JSVa
         global,
         frame,
         b"input.xml",
-        true,
-        true,
-        true,
+        super::BlobOrBufferInput::Bytes,
+        super::NullishInput::Throw,
+        super::StringInput::AsIs,
         |arena, log, source, source_encoding| {
             let encoding = match source_encoding {
                 super::SourceEncoding::Bytes => xml::InputEncoding::Bytes,
diff --git a/src/runtime/api/YAMLObject.rs b/src/runtime/api/YAMLObject.rs
index 06ab34da89da..b5ac84aa14e9 100644
--- a/src/runtime/api/YAMLObject.rs
+++ b/src/runtime/api/YAMLObject.rs
@@ -1026,13 +1026,13 @@ fn is_inf_suffix(str: &BunString, i: usize) -> bool {
 
 #[bun_jsc::host_fn]
 pub(crate) fn parse(global: &JSGlobalObject, call_frame: &CallFrame) -> JsResult<JSValue> {
-    // reject_nullish=false preserves YAML's coerce-undefined-to-"undefined" behavior.
+    // `NullishInput::ToString` preserves YAML's coerce-undefined-to-"undefined" behavior.
     super::with_text_format_source(
         global,
         call_frame,
         b"input.yaml",
-        true,
-        false,
+        super::BlobOrBufferInput::Bytes,
+        super::NullishInput::ToString,
         |arena, log, source| {
             // `ParserCtx::to_js` materializes each `E::Array`/`E::Object`
             // once by pointer identity, so a cyclic graph is fine here.
diff --git a/test/js/bun/jsonc/jsonc.test.ts b/test/js/bun/jsonc/jsonc.test.ts
index bce489dde5d9..d42e1d6646ed 100644
--- a/test/js/bun/jsonc/jsonc.test.ts
+++ b/test/js/bun/jsonc/jsonc.test.ts
@@ -140,6 +140,22 @@ test("Bun.JSONC.parse throws a SyntaxError on invalid input", () => {
   }
 });
 
+test("Bun.JSONC.parse throws on undefined and null input", () => {
+  expect(() => Bun.JSONC.parse(undefined as any)).toThrow("Expected a string to parse");
+  expect(() => (Bun.JSONC.parse as any)()).toThrow("Expected a string to parse");
+  expect(() => Bun.JSONC.parse(null as any)).toThrow("Expected a string to parse");
+});
+
+test("Bun.JSONC.parse stringifies non-string input like JSON.parse does", () => {
+  expect(Bun.JSONC.parse(42 as any)).toBe(42);
+  expect(Bun.JSONC.parse({ toString: () => "[1, 2,] // ok" } as any)).toEqual([1, 2]);
+  // A Buffer stringifies to its text; a Blob stringifies to "[object Blob]"
+  // rather than being read as bytes (unlike Bun.TOML.parse and friends).
+  expect(Bun.JSONC.parse(Buffer.from('{"a": 1, /* c */}') as any)).toEqual({ a: 1 });
+  expect(() => Bun.JSONC.parse(new Blob(['{"a": 1}']) as any)).toThrow(SyntaxError);
+  expect(() => JSON.parse(new Blob(['{"a": 1}']) as any)).toThrow(SyntaxError);
+});
+
 test("Bun.JSONC.parse SyntaxError names the actual error, not a preceding warning", () => {
   let thrown: unknown;
   try {
diff --git a/test/js/bun/yaml/yaml.test.ts b/test/js/bun/yaml/yaml.test.ts
index db877dbca7df..5c6851b1b605 100644
--- a/test/js/bun/yaml/yaml.test.ts
+++ b/test/js/bun/yaml/yaml.test.ts
@@ -317,6 +317,15 @@ development:
         });
       });
 
+      test("stringifies any other input instead of throwing, undefined and null included", () => {
+        // Unlike TOML/JSONC/JSON5/XML, YAML.parse(undefined) parses the text "undefined".
+        expect(YAML.parse(undefined as any)).toBe("undefined");
+        expect((YAML.parse as any)()).toBe("undefined");
+        expect(YAML.parse(null as any)).toBe(null);
+        expect(YAML.parse(42 as any)).toBe(42);
+        expect(YAML.parse({ toString: () => "a: 1" } as any)).toEqual({ a: 1 });
+      });
+
       test("complex nested structure from various input types", () => {
         const complexYaml = `
 version: "1.0"