diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 5227346aeb..22635d2927 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -218,6 +218,35 @@ clamp_row_est(double nrows)
 	return nrows;
 }
 
+/*
+ * clamp_width_est
+ *		Force a tuple-width estimate to a sane value.
+ *
+ * The planner represents datatype width and tuple width estimates as int32.
+ * When summing column width estimates to create a tuple width estimate,
+ * it's possible to reach integer overflow in edge cases.  To ensure sane
+ * behavior, we form such sums in int64 arithmetic and then apply this routine
+ * to clamp to int32 range.
+ */
+int32
+clamp_width_est(int64 tuple_width)
+{
+	/*
+	 * Anything more than MaxAllocSize is clearly bogus, since we could not
+	 * create a tuple that large.
+	 */
+	if (tuple_width > MaxAllocSize)
+		return (int32) MaxAllocSize;
+
+	/*
+	 * Unlike clamp_row_est, we just Assert that the value isn't negative,
+	 * rather than masking such errors.
+	 */
+	Assert(tuple_width >= 0);
+
+	return (int32) tuple_width;
+}
+
 /*
  * clamp_cardinality_to_long
  *		Cast a Cardinality value to a sane long value.
@@ -6101,7 +6130,7 @@ static void
 set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 {
 	Oid			reloid = planner_rt_fetch(rel->relid, root)->relid;
-	int32		tuple_width = 0;
+	int64		tuple_width = 0;
 	bool		have_wholerow_var = false;
 	ListCell   *lc;
 
@@ -6213,7 +6242,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 	 */
 	if (have_wholerow_var)
 	{
-		int32		wholerow_width = MAXALIGN(SizeofHeapTupleHeader);
+		int64		wholerow_width = MAXALIGN(SizeofHeapTupleHeader);
 
 		if (reloid != InvalidOid)
 		{
@@ -6230,7 +6259,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 				wholerow_width += rel->attr_widths[i - rel->min_attr];
 		}
 
-		rel->attr_widths[0 - rel->min_attr] = wholerow_width;
+		rel->attr_widths[0 - rel->min_attr] = clamp_width_est(wholerow_width);
 
 		/*
 		 * Include the whole-row Var as part of the output tuple.  Yes, that
@@ -6239,8 +6268,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 		tuple_width += wholerow_width;
 	}
 
-	Assert(tuple_width >= 0);
-	rel->reltarget->width = tuple_width;
+	rel->reltarget->width = clamp_width_est(tuple_width);
 }
 
 /*
@@ -6258,7 +6286,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 PathTarget *
 set_pathtarget_cost_width(PlannerInfo *root, PathTarget *target)
 {
-	int32		tuple_width = 0;
+	int64		tuple_width = 0;
 	ListCell   *lc;
 
 	/* Vars are assumed to have cost zero, but other exprs do not */
@@ -6282,8 +6310,7 @@ set_pathtarget_cost_width(PlannerInfo *root, PathTarget *target)
 		}
 	}
 
-	Assert(tuple_width >= 0);
-	target->width = tuple_width;
+	target->width = clamp_width_est(tuple_width);
 
 	return target;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index a8cea5efe1..6f45efde21 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -4610,6 +4610,7 @@ create_one_window_path(PlannerInfo *root,
 			 * Note: a WindowFunc adds nothing to the target's eval costs; but
 			 * we do need to account for the increase in tlist width.
 			 */
+			int64		tuple_width = window_target->width;
 			ListCell   *lc2;
 
 			window_target = copy_pathtarget(window_target);
@@ -4618,8 +4619,9 @@ create_one_window_path(PlannerInfo *root,
 				WindowFunc *wfunc = lfirst_node(WindowFunc, lc2);
 
 				add_column_to_pathtarget(window_target, (Expr *) wfunc, 0);
-				window_target->width += get_typavgwidth(wfunc->wintype, -1);
+				tuple_width += get_typavgwidth(wfunc->wintype, -1);
 			}
+			window_target->width = clamp_width_est(tuple_width);
 		}
 		else
 		{
diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index b1723578e6..66b5e2b1e7 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -375,6 +375,7 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 							SpecialJoinInfo *sjinfo)
 {
 	Relids		relids = joinrel->relids;
+	int64		tuple_width = joinrel->reltarget->width;
 	ListCell   *lc;
 
 	foreach(lc, root->placeholder_list)
@@ -419,7 +420,7 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 					cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);
 					joinrel->reltarget->cost.startup += cost.startup;
 					joinrel->reltarget->cost.per_tuple += cost.per_tuple;
-					joinrel->reltarget->width += phinfo->ph_width;
+					tuple_width += phinfo->ph_width;
 				}
 			}
 
@@ -443,6 +444,8 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 								phinfo->ph_lateral);
 		}
 	}
+
+	joinrel->reltarget->width = clamp_width_est(tuple_width);
 }
 
 /*
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 7159c775fb..0e35b9d0ab 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -1137,7 +1137,7 @@ estimate_rel_size(Relation rel, int32 *attr_widths,
 int32
 get_rel_data_width(Relation rel, int32 *attr_widths)
 {
-	int32		tuple_width = 0;
+	int64		tuple_width = 0;
 	int			i;
 
 	for (i = 1; i <= RelationGetNumberOfAttributes(rel); i++)
@@ -1167,7 +1167,7 @@ get_rel_data_width(Relation rel, int32 *attr_widths)
 		tuple_width += item_width;
 	}
 
-	return tuple_width;
+	return clamp_width_est(tuple_width);
 }
 
 /*
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 5d83f60eb9..9dfeb4ffd4 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -22,6 +22,7 @@
 #include "optimizer/clauses.h"
 #include "optimizer/cost.h"
 #include "optimizer/inherit.h"
+#include "optimizer/optimizer.h"
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "optimizer/placeholder.h"
@@ -1092,6 +1093,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 					bool can_null)
 {
 	Relids		relids = joinrel->relids;
+	int64		tuple_width = joinrel->reltarget->width;
 	ListCell   *vars;
 	ListCell   *lc;
 
@@ -1144,7 +1146,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
 													phv);
 				/* Bubbling up the precomputed result has cost zero */
-				joinrel->reltarget->width += phinfo->ph_width;
+				tuple_width += phinfo->ph_width;
 			}
 			continue;
 		}
@@ -1165,7 +1167,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 				list_nth(root->row_identity_vars, var->varattno - 1);
 
 			/* Update reltarget width estimate from RowIdentityVarInfo */
-			joinrel->reltarget->width += ridinfo->rowidwidth;
+			tuple_width += ridinfo->rowidwidth;
 		}
 		else
 		{
@@ -1181,7 +1183,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 				continue;		/* nope, skip it */
 
 			/* Update reltarget width estimate from baserel's attr_widths */
-			joinrel->reltarget->width += baserel->attr_widths[ndx];
+			tuple_width += baserel->attr_widths[ndx];
 		}
 
 		/*
@@ -1221,6 +1223,8 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 
 		/* Vars have cost zero, so no need to adjust reltarget->cost */
 	}
+
+	joinrel->reltarget->width = clamp_width_est(tuple_width);
 }
 
 /*
diff --git a/src/include/optimizer/optimizer.h b/src/include/optimizer/optimizer.h
index 6e8b81c51d..da50044bf1 100644
--- a/src/include/optimizer/optimizer.h
+++ b/src/include/optimizer/optimizer.h
@@ -90,6 +90,7 @@ extern PGDLLIMPORT double recursive_worktable_factor;
 extern PGDLLIMPORT int effective_cache_size;
 
 extern double clamp_row_est(double nrows);
+extern int32 clamp_width_est(int64 tuple_width);
 extern long clamp_cardinality_to_long(Cardinality x);
 
 /* in path/indxpath.c: */