diff --git a/crates/uv/src/commands/project/export.rs b/crates/uv/src/commands/project/export.rs
index 32d68bb59dbbd..2d01d79248e7f 100644
--- a/crates/uv/src/commands/project/export.rs
+++ b/crates/uv/src/commands/project/export.rs
@@ -4,6 +4,7 @@ use std::io::Write;
 use std::path::{Path, PathBuf};
 
 use anyhow::{Context, Result, anyhow};
+use clap::ValueEnum;
 use itertools::Itertools;
 use owo_colors::OwoColorize;
 
@@ -291,6 +292,22 @@ pub(crate) async fn export(
     target.validate_extras(&extras)?;
     target.validate_groups(&groups)?;
 
+    if output_file
+        .as_deref()
+        .and_then(Path::file_name)
+        .is_some_and(|name| name.eq_ignore_ascii_case("pyproject.toml"))
+    {
+        return Err(anyhow!(
+            "`pyproject.toml` is not a supported output format for `{}` (supported formats: {})",
+            "uv export".green(),
+            ExportFormat::value_variants()
+                .iter()
+                .filter_map(clap::ValueEnum::to_possible_value)
+                .map(|value| value.get_name().to_string())
+                .join(", ")
+        ));
+    }
+
     // Write the resolved dependencies to the output channel.
     let mut writer = OutputWriter::new(!quiet || output_file.is_none(), output_file.as_deref());
 
diff --git a/crates/uv/tests/it/export.rs b/crates/uv/tests/it/export.rs
index 1f40ae859a506..c1b96bb47aee3 100644
--- a/crates/uv/tests/it/export.rs
+++ b/crates/uv/tests/it/export.rs
@@ -4482,29 +4482,14 @@ fn pep_751_infer_output_format() -> Result<()> {
     Resolved 4 packages in [TIME]
     "#);
 
-    // TODO(charlie): Error on `pyproject.toml`. Right now, it's treated as `requirements.txt`.
     uv_snapshot!(context.filters(), context.export().arg("-o").arg("pyproject.toml"), @r"
-    success: true
-    exit_code: 0
+    success: false
+    exit_code: 2
     ----- stdout -----
-    # This file was autogenerated by uv via the following command:
-    #    uv export --cache-dir [CACHE_DIR] -o pyproject.toml
-    -e .
-    anyio==3.7.0 \
-        --hash=sha256:275d9973793619a5374e1c89a4f4ad3f4b0a5510a2b5b939444bee8f4c4d37ce \
-        --hash=sha256:eddca883c4175f14df8aedce21054bfca3adb70ffe76a9f607aef9d7fa2ea7f0
-        # via project
-    idna==3.6 \
-        --hash=sha256:9ecdbbd083b06798ae1e86adcbfe8ab1479cf864e4ee30fe4e46a003d12491ca \
-        --hash=sha256:c05567e9c24a6b9faaa835c4821bad0590fbb9d5779e7caa6e1cc4978e7eb24f
-        # via anyio
-    sniffio==1.3.1 \
-        --hash=sha256:2f6da418d1f1e0fddd844478f41680e794e6051915791a034ff65e5f100525a2 \
-        --hash=sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc
-        # via anyio
 
     ----- stderr -----
     Resolved 4 packages in [TIME]
+    error: `pyproject.toml` is not a supported output format for `uv export` (supported formats: requirements.txt, pylock.toml, cyclonedx1.5)
     ");
 
     Ok(())