diff --git a/midas/checker/frame_methods.py b/midas/checker/frame_methods.py
index c2935f8..7472bf4 100644
--- a/midas/checker/frame_methods.py
+++ b/midas/checker/frame_methods.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import ast
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, Callable, Optional
 
@@ -39,6 +40,7 @@ def frame_method(*names: str):
 @dataclass(frozen=True, kw_only=True)
 class Call:
     location: Location
+    call_expr: p.Expr
     frame: DataFrameType
     frame_expr: p.Expr
     positional: list[TypedExpr]
@@ -174,6 +176,11 @@ class MethodRegistry(metaclass=_MethodRegistryMeta):
             positional=call.positional,
             keywords=call.keywords,
         )
+        if result.is_valid:
+            self._assert_same_length(
+                call.call_expr, call.frame_expr, call.positional[0][0]
+            )
+
         return result.result
 
     @frame_method()
@@ -214,3 +221,50 @@ class MethodRegistry(metaclass=_MethodRegistryMeta):
             keywords=call.keywords,
         )
         return result.result
+
+    def _assert_same_length(self, call_expr: p.Expr, frame1: p.Expr, frame2: p.Expr):
+        func_name: str = "__midas_frame_same_length__"
+        self.assertions.define(
+            func_name,
+            ast.FunctionDef(
+                name=func_name,
+                args=ast.arguments(
+                    posonlyargs=[],
+                    args=[
+                        ast.arg(arg="frame1"),
+                        ast.arg(arg="frame2"),
+                    ],
+                    kwonlyargs=[],
+                    defaults=[],
+                    kw_defaults=[],
+                ),
+                body=[
+                    ast.Return(
+                        value=ast.Compare(
+                            left=ast.Attribute(
+                                value=ast.Name(id="frame1"),
+                                attr="size",
+                            ),
+                            ops=[ast.Eq()],
+                            comparators=[
+                                ast.Attribute(
+                                    value=ast.Name(id="frame2"),
+                                    attr="size",
+                                )
+                            ],
+                        )
+                    )
+                ],
+                decorator_list=[],
+            ),
+        )
+        self.assertions.add(
+            bound_expr=call_expr,
+            inputs=[frame1, frame2],
+            builder=lambda f1, f2: ast.Call(
+                func=ast.Name(id=func_name),
+                args=[f1, f2],
+                keywords=[],
+            ),
+            message="DataFrames must have the same length",
+        )
diff --git a/midas/checker/frames.py b/midas/checker/frames.py
index 56c34c6..1a1a917 100644
--- a/midas/checker/frames.py
+++ b/midas/checker/frames.py
@@ -141,6 +141,7 @@ class FrameManager:
         self,
         method: str,
         location: Location,
+        call_expr: p.Expr,
         frame: DataFrameType,
         frame_expr: p.Expr,
         positional: list[TypedExpr],
@@ -148,6 +149,7 @@ class FrameManager:
     ) -> Type:
         call: Call = Call(
             location=location,
+            call_expr=call_expr,
             frame=frame,
             frame_expr=frame_expr,
             positional=positional,
diff --git a/midas/checker/python.py b/midas/checker/python.py
index a42115f..2e0a07c 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -212,6 +212,7 @@ class PythonTyper(
     def call_method(
         self,
         location: Location,
+        call_expr: p.Expr,
         obj: TypedExpr,
         method_name: str,
         positional: list[TypedExpr],
@@ -223,6 +224,7 @@ class PythonTyper(
                 return self.frame_mgr.call(
                     method=method_name,
                     location=location,
+                    call_expr=call_expr,
                     frame=unfolded,
                     frame_expr=obj[0],
                     positional=positional,
@@ -503,7 +505,9 @@ class PythonTyper(
             )
             return UnknownType()
 
-        return self._visit_binary_expr(expr.location, expr.left, expr.right, method)
+        return self._visit_binary_expr(
+            expr.location, expr, expr.left, expr.right, method
+        )
 
     def visit_compare_expr(self, expr: p.CompareExpr) -> Type:
         method: Optional[str] = PY_COMPARATOR_METHODS.get(expr.operator.__class__)
@@ -514,10 +518,17 @@ class PythonTyper(
             )
             return UnknownType()
 
-        return self._visit_binary_expr(expr.location, expr.left, expr.right, method)
+        return self._visit_binary_expr(
+            expr.location, expr, expr.left, expr.right, method
+        )
 
     def _visit_binary_expr(
-        self, location: Location, left_expr: p.Expr, right_expr: p.Expr, method: str
+        self,
+        location: Location,
+        expr: p.Expr,
+        left_expr: p.Expr,
+        right_expr: p.Expr,
+        method: str,
     ) -> Type:
         left: Type = self.type_of(left_expr)
         right: Type = self.type_of(right_expr)
@@ -525,7 +536,12 @@ class PythonTyper(
         result: Optional[Type]
         try:
             result = self.call_method(
-                location, (left_expr, left), method, [(right_expr, right)], {}
+                location=location,
+                call_expr=expr,
+                obj=(left_expr, left),
+                method_name=method,
+                positional=[(right_expr, right)],
+                keywords={},
             )
         except UndefinedMethodException:
             self.reporter.error(
@@ -550,7 +566,12 @@ class PythonTyper(
         result: Optional[Type]
         try:
             result = self.call_method(
-                expr.location, (expr.right, operand), method, [], {}
+                location=expr.location,
+                call_expr=expr,
+                obj=(expr.right, operand),
+                method_name=method,
+                positional=[],
+                keywords={},
             )
         except UndefinedMethodException:
             self.reporter.error(
@@ -581,6 +602,7 @@ class PythonTyper(
                     return self.frame_mgr.call(
                         method=method,
                         location=expr.location,
+                        call_expr=expr,
                         frame=unfolded,
                         frame_expr=obj,
                         positional=positional,