diff --git a/Cargo.lock b/Cargo.lock
index 1768589..012da77 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -253,7 +253,7 @@ checksum = "7fcaabb2fef8c910e7f4c7ce9f67a1283a1715879a7c230ca9d6d1ae31f16d91"
 [[package]]
 name = "els"
 version = "0.1.18"
-source = "git+https://github.com/erg-lang/erg?branch=main#f604338d996fdee827c51386e23b26b6c0159389"
+source = "git+https://github.com/erg-lang/erg?branch=main#f86a4498465aa8a5a0068dfb4a235596f9da462b"
 dependencies = [
  "erg_common",
  "erg_compiler",
@@ -274,7 +274,7 @@ dependencies = [
 [[package]]
 name = "erg_common"
 version = "0.6.6"
-source = "git+https://github.com/erg-lang/erg?branch=main#f604338d996fdee827c51386e23b26b6c0159389"
+source = "git+https://github.com/erg-lang/erg?branch=main#f86a4498465aa8a5a0068dfb4a235596f9da462b"
 dependencies = [
  "backtrace-on-stack-overflow",
  "hermit-abi",
@@ -285,7 +285,7 @@ dependencies = [
 [[package]]
 name = "erg_compiler"
 version = "0.6.6"
-source = "git+https://github.com/erg-lang/erg?branch=main#f604338d996fdee827c51386e23b26b6c0159389"
+source = "git+https://github.com/erg-lang/erg?branch=main#f86a4498465aa8a5a0068dfb4a235596f9da462b"
 dependencies = [
  "erg_common",
  "erg_parser",
@@ -294,7 +294,7 @@ dependencies = [
 [[package]]
 name = "erg_parser"
 version = "0.6.6"
-source = "git+https://github.com/erg-lang/erg?branch=main#f604338d996fdee827c51386e23b26b6c0159389"
+source = "git+https://github.com/erg-lang/erg?branch=main#f86a4498465aa8a5a0068dfb4a235596f9da462b"
 dependencies = [
  "erg_common",
  "unicode-xid 0.2.4",
diff --git a/src/analyze.rs b/src/analyze.rs
index 77c5fa7..b8ac87e 100644
--- a/src/analyze.rs
+++ b/src/analyze.rs
@@ -125,8 +125,11 @@ impl PythonAnalyzer {
             Err(iart) => {
                 errors.extend(iart.errors);
                 let errors = handle_err::filter_errors(self.checker.get_mod_ctx(), errors);
+                let (errors, _warns) =
+                    handle_err::downgrade_errors(self.checker.get_mod_ctx(), errors);
                 warns.extend(iart.warns);
-                let warns = handle_err::filter_errors(self.checker.get_mod_ctx(), warns);
+                let mut warns = handle_err::filter_errors(self.checker.get_mod_ctx(), warns);
+                warns.extend(_warns);
                 Err(IncompleteArtifact::new(iart.object, errors, warns))
             }
         }
diff --git a/src/handle_err.rs b/src/handle_err.rs
index 479a6d1..0806f28 100644
--- a/src/handle_err.rs
+++ b/src/handle_err.rs
@@ -1,8 +1,18 @@
 use erg_common::error::ErrorKind;
 use erg_common::log;
+use erg_common::traits::Stream;
+use erg_common::Str;
 // use erg_common::style::{remove_style, StyledString, Color};
 use erg_compiler::context::ModuleContext;
-use erg_compiler::error::{CompileError, CompileErrors};
+use erg_compiler::error::{CompileError, CompileErrors, CompileWarning, CompileWarnings};
+
+pub fn default_implementations(op: &str) -> Option<&str> {
+    match op {
+        "`==`" => Some("__eq__"),
+        "`!=`" => Some("__ne__"),
+        _ => None,
+    }
+}
 
 pub(crate) fn filter_errors(ctx: &ModuleContext, errors: CompileErrors) -> CompileErrors {
     errors
@@ -35,3 +45,48 @@ fn filter_error(_ctx: &ModuleContext, error: CompileError) -> Option<CompileErro
         _ => Some(error),
     }
 }
+
+pub(crate) fn downgrade_errors(
+    ctx: &ModuleContext,
+    errors: CompileErrors,
+) -> (CompileErrors, CompileWarnings) {
+    let mut errs = CompileErrors::empty();
+    let mut warns = CompileWarnings::empty();
+    for error in errors {
+        match downgrade_error(ctx, error) {
+            Ok(err) => errs.push(err),
+            Err(warn) => warns.push(warn),
+        }
+    }
+    (errs, warns)
+}
+
+#[allow(clippy::result_large_err)]
+fn downgrade_error(
+    _ctx: &ModuleContext,
+    mut error: CompileError,
+) -> Result<CompileError, CompileWarning> {
+    match error.core.kind {
+        ErrorKind::TypeError => {
+            // TODO: trim escape sequences
+            let callee = Str::rc(
+                error
+                    .core
+                    .main_message
+                    .trim_start_matches("the type of ")
+                    .trim_end_matches(" is mismatched"),
+            );
+            if let Some(op) = callee.find_sub(&["`==`", "`!=`"]) {
+                error.core.main_message = format!(
+                    "this object does not implement `{}`",
+                    default_implementations(op).unwrap()
+                );
+                error.core.kind = ErrorKind::TypeWarning;
+                Err(error)
+            } else {
+                Ok(error)
+            }
+        }
+        _ => Ok(error),
+    }
+}