diff --git a/crates/fayalite/src/cli.rs b/crates/fayalite/src/cli.rs
index 66741ef..1f208a8 100644
--- a/crates/fayalite/src/cli.rs
+++ b/crates/fayalite/src/cli.rs
@@ -258,7 +258,7 @@ pub struct VerilogArgs {
         default_value = "firtool",
         env = "FIRTOOL",
         value_hint = ValueHint::CommandName,
-        value_parser = OsStringValueParser::new().try_map(which::which)
+        value_parser = OsStringValueParser::new().try_map(which)
     )]
     pub firtool: PathBuf,
     #[arg(long)]
@@ -428,6 +428,13 @@ impl clap::Args for FormalAdjustArgs {
     }
 }
 
+fn which(v: std::ffi::OsString) -> which::Result<PathBuf> {
+    #[cfg(not(miri))]
+    return which::which(v);
+    #[cfg(miri)]
+    return Ok(Path::new("/").join(v));
+}
+
 #[derive(Parser, Clone)]
 #[non_exhaustive]
 pub struct FormalArgs {
@@ -438,7 +445,7 @@ pub struct FormalArgs {
         default_value = "sby",
         env = "SBY",
         value_hint = ValueHint::CommandName,
-        value_parser = OsStringValueParser::new().try_map(which::which)
+        value_parser = OsStringValueParser::new().try_map(which)
     )]
     pub sby: PathBuf,
     #[arg(long)]