diff --git a/crates/erg_common/config.rs b/crates/erg_common/config.rs
index be706528..8fa97f4f 100644
--- a/crates/erg_common/config.rs
+++ b/crates/erg_common/config.rs
@@ -179,6 +179,7 @@ pub struct ErgConfig {
     pub packages: ArcArray<Package>,
     pub effect_check: bool,
     pub ownership_check: bool,
+    pub use_pylyzer: bool,
 }
 
 impl Default for ErgConfig {
@@ -206,6 +207,7 @@ impl Default for ErgConfig {
             packages: ArcArray::from([]),
             effect_check: true,
             ownership_check: true,
+            use_pylyzer: false,
         }
     }
 }
@@ -340,6 +342,9 @@ impl ErgConfig {
                         None,
                     ));
                 }
+                "--use-pylyzer" => {
+                    cfg.use_pylyzer = true;
+                }
                 "--use-local-package" => {
                     let name = args
                         .next()
diff --git a/crates/erg_compiler/build_package.rs b/crates/erg_compiler/build_package.rs
index d7a25f26..fc16f952 100644
--- a/crates/erg_compiler/build_package.rs
+++ b/crates/erg_compiler/build_package.rs
@@ -630,36 +630,39 @@ impl<ASTBuilder: ASTBuildable, HIRBuilder: Buildable>
             if self.cfg.input.path() == path.as_path() {
                 return Ok(path);
             }
-            let (out, err) = if self.cfg.mode == ErgMode::LanguageServer || self.cfg.quiet_repl {
-                (Stdio::null(), Stdio::null())
-            } else {
-                (Stdio::inherit(), Stdio::inherit())
-            };
-            // pylyzer is a static analysis tool for Python (https://github.com/mtshiba/pylyzer).
-            // It can convert a Python script to an Erg AST for code analysis.
-            // There is also an option to output the analysis result as `d.er`. Use this if the system have pylyzer installed.
-            // A type definition file may be generated even if not all type checks succeed.
-            if let Ok(status) = Command::new("pylyzer")
-                .arg("--dump-decl")
-                .arg(path.to_str().unwrap_or_default())
-                .stdout(out)
-                .stderr(err)
-                .spawn()
-                .and_then(|mut child| child.wait())
-            {
-                if let Some(path) = self
-                    .cfg
-                    .input
-                    .resolve_decl_path(Path::new(&__name__[..]), &self.cfg)
+            if self.cfg.use_pylyzer {
+                let (out, err) = if self.cfg.mode == ErgMode::LanguageServer || self.cfg.quiet_repl
                 {
-                    let size = metadata(&path).or(Err(()))?.len();
-                    // if pylyzer crashed
-                    if !status.success() && size == 0 {
-                        // The presence of the decl file indicates that the analysis is in progress or completed,
-                        // so if pylyzer crashes in the middle of the analysis, delete the file.
-                        remove_file(&path).unwrap();
-                    } else {
-                        return Ok(path);
+                    (Stdio::null(), Stdio::null())
+                } else {
+                    (Stdio::inherit(), Stdio::inherit())
+                };
+                // pylyzer is a static analysis tool for Python (https://github.com/mtshiba/pylyzer).
+                // It can convert a Python script to an Erg AST for code analysis.
+                // There is also an option to output the analysis result as `d.er`. Use this if the system have pylyzer installed.
+                // A type definition file may be generated even if not all type checks succeed.
+                if let Ok(status) = Command::new("pylyzer")
+                    .arg("--dump-decl")
+                    .arg(path.to_str().unwrap_or_default())
+                    .stdout(out)
+                    .stderr(err)
+                    .spawn()
+                    .and_then(|mut child| child.wait())
+                {
+                    if let Some(path) = self
+                        .cfg
+                        .input
+                        .resolve_decl_path(Path::new(&__name__[..]), &self.cfg)
+                    {
+                        let size = metadata(&path).or(Err(()))?.len();
+                        // if pylyzer crashed
+                        if !status.success() && size == 0 {
+                            // The presence of the decl file indicates that the analysis is in progress or completed,
+                            // so if pylyzer crashes in the middle of the analysis, delete the file.
+                            remove_file(&path).unwrap();
+                        } else {
+                            return Ok(path);
+                        }
                     }
                 }
             }
diff --git a/crates/erg_compiler/module/graph.rs b/crates/erg_compiler/module/graph.rs
index 65412e73..93e2288c 100644
--- a/crates/erg_compiler/module/graph.rs
+++ b/crates/erg_compiler/module/graph.rs
@@ -1,5 +1,6 @@
 use std::fmt;
 
+use erg_common::consts::DEBUG_MODE;
 use erg_common::pathutil::NormalizedPathBuf;
 use erg_common::set;
 use erg_common::set::Set;
@@ -95,6 +96,12 @@ impl ModuleGraph {
     }
 
     pub fn add_node_if_none(&mut self, path: &NormalizedPathBuf) {
+        if path.is_dir() {
+            if DEBUG_MODE {
+                panic!("path is a directory: {path}");
+            }
+            return;
+        }
         if self.0.iter().all(|n| &n.id != path) {
             let node = Node::new(path.clone(), (), set! {});
             self.0.push(node);
@@ -107,6 +114,12 @@ impl ModuleGraph {
         referrer: &NormalizedPathBuf,
         depends_on: NormalizedPathBuf,
     ) -> Result<(), IncRefError> {
+        if depends_on.is_dir() {
+            if DEBUG_MODE {
+                panic!("path is a directory: {depends_on}");
+            }
+            return Ok(());
+        }
         self.add_node_if_none(referrer);
         if referrer == &depends_on {
             return Ok(());