diff --git a/onihime/src/lib.rs b/onihime/src/lib.rs
index 47d0387..f030f2d 100644
--- a/onihime/src/lib.rs
+++ b/onihime/src/lib.rs
@@ -1,6 +1,11 @@
 //! Onihime programming language.
 
-#![deny(missing_debug_implementations, missing_docs, rust_2018_idioms)]
+#![deny(
+    missing_debug_implementations,
+    missing_docs,
+    rust_2018_idioms,
+    unsafe_code
+)]
 
 mod lexer;
 mod parser;
diff --git a/onihime/src/parser/ast.rs b/onihime/src/parser/ast.rs
index 82a326d..5c2f5bb 100644
--- a/onihime/src/parser/ast.rs
+++ b/onihime/src/parser/ast.rs
@@ -1,4 +1,4 @@
-use super::error::{ParserError, ParserErrorKind};
+use super::error::ParserError;
 use crate::{
     lexer::{Symbol, Token, TokenKind},
     span::Span,
diff --git a/onihime/src/parser/mod.rs b/onihime/src/parser/mod.rs
index 4fc5ad2..e8874b3 100644
--- a/onihime/src/parser/mod.rs
+++ b/onihime/src/parser/mod.rs
@@ -42,7 +42,7 @@ impl<'parser> Parser<'parser> {
         // run out of tokens, or an error occurs:
         while !self.lexer.eof() {
             if let Some(node) = self.expr()? {
-                self.current.push_node(node);
+                self.current.push_node(node)?;
             }
         }
 
@@ -88,7 +88,7 @@ impl<'parser> Parser<'parser> {
                     let node = Node::try_from(token)?;
                     let span = node.span.clone();
 
-                    self.current.push_node(node);
+                    self.current.push_node(node)?;
                     self.current.span.extend(&span);
 
                     Ok(None)
@@ -160,7 +160,7 @@ mod tests {
         ( $name:ident: $input:literal, $src:ident => $ast:expr ) => {
             #[test]
             fn $name() {
-                let mut parser = Parser::new($input);
+                let parser = Parser::new($input);
                 let $src = parser.lexer.source();
                 assert_eq!(parser.parse(), $ast);
             }
diff --git a/onihime/src/span.rs b/onihime/src/span.rs
index c2b7cf5..164d714 100644
--- a/onihime/src/span.rs
+++ b/onihime/src/span.rs
@@ -197,4 +197,33 @@ mod tests {
         assert_eq!(source.get_line(1), "line 2");
         assert_eq!(source.get_line(2), "line 3");
     }
+
+    #[test]
+    fn span_partial_eq() {
+        let source = Arc::new(Source::new(None, String::new()));
+
+        let a = Span::new(0..0, source.clone());
+        assert_eq!(a, a);
+
+        let b = Span::new(1..10, source.clone());
+        assert_ne!(a, b);
+
+        let source2 = Arc::new(Source::new(None, String::from("foo")));
+        let c = Span::new(0..0, source2.clone());
+        assert_ne!(a, c);
+    }
+
+    #[test]
+    fn span_start_end_location() {
+        let source = Arc::new(Source::new(None, "foo\nbar\nbaz".into()));
+        let span = Span::new(2..9, source);
+
+        let start = span.location();
+        assert_eq!(start.line, 0);
+        assert_eq!(start.column, 2);
+
+        let end = span.end_location();
+        assert_eq!(end.line, 2);
+        assert_eq!(end.column, 1);
+    }
 }