diff --git i/src/backend/executor/execExpr.c w/src/backend/executor/execExpr.c
index f1569879b52..2972af3c189 100644
--- i/src/backend/executor/execExpr.c
+++ w/src/backend/executor/execExpr.c
@@ -346,6 +346,7 @@ ExecInitExprList(List *nodes, PlanState *parent)
 
 	return result;
 }
+#include "nodes/print.h"
 
 /*
  *		ExecBuildProjectionInfo
@@ -399,6 +400,24 @@ ExecBuildProjectionInfo(List *targetList,
 		AttrNumber	attnum = 0;
 		bool		isSafeVar = false;
 
+		if (slot && tle->expr != NULL)
+		{
+			Oid expr_type = exprType((Node *) tle->expr);
+			Form_pg_attribute slot_attr = TupleDescAttr(slot->tts_tupleDescriptor, tle->resno - 1);
+			Oid slot_type = slot_attr->atttypid;
+
+			if (expr_type != slot_type)
+			{
+				elog(WARNING, "type mismatch: resno %d: slot (type: %d, name: %s) vs expr (type: %d, name: %s)",
+					 tle->resno, slot_type,
+					 NameStr(slot_attr->attname),
+					 expr_type,
+					 tle->resname
+					);
+				elog_node_display(WARNING, "TargetEntry", tle, true);
+			}
+		}
+
 		/*
 		 * If tlist expression is a safe non-system Var, use the fast-path
 		 * ASSIGN_*_VAR opcodes.  "Safe" means that we don't need to apply