diff --git a/build/ninja_gen/src/python.rs b/build/ninja_gen/src/python.rs
index 3d6433ce3..37af902de 100644
--- a/build/ninja_gen/src/python.rs
+++ b/build/ninja_gen/src/python.rs
@@ -124,7 +124,7 @@ pub struct PythonEnvironment {
 impl BuildAction for PythonEnvironment {
     fn command(&self) -> &str {
         if env::var("OFFLINE_BUILD").is_err() {
-            "$runner pyenv $uv_binary $builddir/$pyenv_folder -- $extra_args"
+            "$runner pyenv $uv_binary $builddir/$pyenv_folder $python -- $extra_args"
         } else {
             "echo 'OFFLINE_BUILD is set. Using the existing PythonEnvironment.'"
         }
@@ -148,18 +148,15 @@ impl BuildAction for PythonEnvironment {
 
             // Set --python flag to .python-version (--no-config ignores it)
             // override if PYTHON_BINARY is set
-            let mut args = self.extra_args.to_string();
-            if let Ok(python_binary) = env::var("PYTHON_BINARY") {
-                args = format!("--python {python_binary} {args}");
-            } else {
+            let python = env::var("PYTHON_BINARY").unwrap_or_else(|_| {
                 let python_version =
                     read_file(".python-version").expect("No .python-version in cwd");
                 let python_version_str =
                     String::from_utf8(python_version).expect("Invalid UTF-8 in .python-version");
-                let python_version_trimmed = python_version_str.trim().to_string();
-                args = format!("--python {python_version_trimmed} {args}");
-            }
-            build.add_variable("extra_args", args);
+                python_version_str.trim().to_string()
+            });
+            build.add_variable("python", python);
+            build.add_variable("extra_args", self.extra_args);
         }
 
         build.add_outputs_ext("bin", bin_path("python"), true);
diff --git a/build/runner/src/pyenv.rs b/build/runner/src/pyenv.rs
index efd58fd91..e919ee5df 100644
--- a/build/runner/src/pyenv.rs
+++ b/build/runner/src/pyenv.rs
@@ -13,6 +13,7 @@ use crate::run::run_command;
 pub struct PyenvArgs {
     uv_bin: String,
     pyenv_folder: String,
+    python: String,
     #[arg(trailing_var_arg = true)]
     extra_args: Vec<String>,
 }
@@ -45,6 +46,7 @@ pub fn setup_pyenv(args: PyenvArgs) {
         command
             .env("UV_PROJECT_ENVIRONMENT", args.pyenv_folder.clone())
             .args(["sync", "--locked", "--no-config"])
+            .args(["--python", &args.python])
             .args(args.extra_args),
     );