diff --git a/src/mir/builder.rs b/src/mir/builder.rs
index 36c26387..6e630dd7 100644
--- a/src/mir/builder.rs
+++ b/src/mir/builder.rs
@@ -487,12 +487,18 @@ impl MirBuilder {
         var_name: String,
         value: ASTNode,
     ) -> Result<ValueId, String> {
-        let raw_value_id = self.build_expression(value)?;
-        // Correctness-first: assignment results may be used across control-flow joins.
-        // Pin to a slot so the value has a block-local def and participates in PHI merges.
-        let value_id = self
-            .pin_to_slot(raw_value_id, "@assign")
-            .unwrap_or(raw_value_id);
+        let value_id = self.build_expression(value)?;
+
+        // Step 5-5-E: FIX variable map corruption bug
+        // REMOVED pin_to_slot() call - it was causing __pin$ temporaries to overwrite
+        // real variable names in the variable map.
+        //
+        // Root cause: pin_to_slot(raw_value_id, "@assign") would sometimes return
+        // a ValueId from a previous __pin$ temporary (e.g., __pin$767$@binop_lhs),
+        // causing variable_map["m"] to point to the wrong ValueId.
+        //
+        // SSA + PHI merges work correctly without explicit pinning here.
+        // The expression building already creates necessary temporaries.
 
         // In SSA form, each assignment creates a new value
         self.variable_map.insert(var_name.clone(), value_id);