diff --git a/src/backend/utils/adt/datum.c b/src/backend/utils/adt/datum.c
index af5944d395..81ea5a48e5 100644
--- a/src/backend/utils/adt/datum.c
+++ b/src/backend/utils/adt/datum.c
@@ -42,6 +42,8 @@
 
 #include "postgres.h"
 
+#include "access/tuptoaster.h"
+#include "fmgr.h"
 #include "utils/datum.h"
 #include "utils/expandeddatum.h"
 
@@ -251,6 +253,61 @@ datumIsEqual(Datum value1, Datum value2, bool typByVal, int typLen)
 	return res;
 }
 
+/*-------------------------------------------------------------------------
+ * datum_image_eq
+ *
+ * Compares two datums for identical contents, based on byte images.  Return
+ * true if the two datums are equal, false otherwise.
+ *-------------------------------------------------------------------------
+ */
+bool
+datum_image_eq(Datum value1, Datum value2, bool typByVal, int typLen)
+{
+	bool		result = true;
+
+	if (typLen == -1)
+	{
+		Size		len1,
+					len2;
+
+		len1 = toast_raw_datum_size(value1);
+		len2 = toast_raw_datum_size(value2);
+		/* No need to de-toast if lengths don't match. */
+		if (len1 != len2)
+			result = false;
+		else
+		{
+			struct varlena *arg1val;
+			struct varlena *arg2val;
+
+			arg1val = PG_DETOAST_DATUM_PACKED(value1);
+			arg2val = PG_DETOAST_DATUM_PACKED(value2);
+
+			result = (memcmp(VARDATA_ANY(arg1val),
+							 VARDATA_ANY(arg2val),
+							 len1 - VARHDRSZ) == 0);
+
+			/* Only free memory if it's a copy made here. */
+			if ((Pointer) arg1val != (Pointer) value1)
+				pfree(arg1val);
+			if ((Pointer) arg2val != (Pointer) value2)
+				pfree(arg2val);
+		}
+	}
+	else if (typByVal)
+	{
+		result = (value1 == value2);
+	}
+	else
+	{
+		result = (memcmp(DatumGetPointer(value1),
+						 DatumGetPointer(value2),
+						 typLen) == 0);
+	}
+
+	return result;
+}
+
 /*-------------------------------------------------------------------------
  * datumEstimateSpace
  *
diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index d715709b7c..b4d0029877 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -42,6 +42,7 @@
 #include "storage/bufmgr.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/inval.h"
@@ -2402,18 +2403,11 @@ ri_KeysEqual(Relation rel, TupleTableSlot *oldslot, TupleTableSlot *newslot,
 			 const RI_ConstraintInfo *riinfo, bool rel_is_pk)
 {
 	const int16 *attnums;
-	const Oid  *eq_oprs;
 
 	if (rel_is_pk)
-	{
 		attnums = riinfo->pk_attnums;
-		eq_oprs = riinfo->pp_eq_oprs;
-	}
 	else
-	{
 		attnums = riinfo->fk_attnums;
-		eq_oprs = riinfo->ff_eq_oprs;
-	}
 
 	/* XXX: could be worthwhile to fetch all necessary attrs at once */
 	for (int i = 0; i < riinfo->nkeys; i++)
@@ -2436,12 +2430,32 @@ ri_KeysEqual(Relation rel, TupleTableSlot *oldslot, TupleTableSlot *newslot,
 		if (isnull)
 			return false;
 
-		/*
-		 * Compare them with the appropriate equality operator.
-		 */
-		if (!ri_AttributesEqual(eq_oprs[i], RIAttType(rel, attnums[i]),
-								oldvalue, newvalue))
-			return false;
+		if (rel_is_pk)
+		{
+			/*
+			 * If we are looking at the PK table, then do a bytewise
+			 * comparison.  We must propagate PK changes if the value is
+			 * changed to one that "looks" different but would compare as
+			 * equal using the equality operator.  This only makes a
+			 * difference for ON UPDATE CASCADE, but for consistency we treat
+			 * all changes to the PK the same.
+			 */
+			Form_pg_attribute att = TupleDescAttr(oldslot->tts_tupleDescriptor, attnums[i] - 1);
+
+			if (!datum_image_eq(oldvalue, newvalue, att->attbyval, att->attlen))
+				return false;
+		}
+		else
+		{
+			/*
+			 * For the FK table, compare with the appropriate equality
+			 * operator.  Changes that compare equal will still satisfy the
+			 * constraint after the update.
+			 */
+			if (!ri_AttributesEqual(riinfo->ff_eq_oprs[i], RIAttType(rel, attnums[i]),
+									oldvalue, newvalue))
+				return false;
+		}
 	}
 
 	return true;
diff --git a/src/backend/utils/adt/rowtypes.c b/src/backend/utils/adt/rowtypes.c
index 5bbf568610..aa7ec8735c 100644
--- a/src/backend/utils/adt/rowtypes.c
+++ b/src/backend/utils/adt/rowtypes.c
@@ -23,6 +23,7 @@
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/typcache.h"
 
@@ -1671,45 +1672,7 @@ record_image_eq(PG_FUNCTION_ARGS)
 			}
 
 			/* Compare the pair of elements */
-			if (att1->attlen == -1)
-			{
-				Size		len1,
-							len2;
-
-				len1 = toast_raw_datum_size(values1[i1]);
-				len2 = toast_raw_datum_size(values2[i2]);
-				/* No need to de-toast if lengths don't match. */
-				if (len1 != len2)
-					result = false;
-				else
-				{
-					struct varlena *arg1val;
-					struct varlena *arg2val;
-
-					arg1val = PG_DETOAST_DATUM_PACKED(values1[i1]);
-					arg2val = PG_DETOAST_DATUM_PACKED(values2[i2]);
-
-					result = (memcmp(VARDATA_ANY(arg1val),
-									 VARDATA_ANY(arg2val),
-									 len1 - VARHDRSZ) == 0);
-
-					/* Only free memory if it's a copy made here. */
-					if ((Pointer) arg1val != (Pointer) values1[i1])
-						pfree(arg1val);
-					if ((Pointer) arg2val != (Pointer) values2[i2])
-						pfree(arg2val);
-				}
-			}
-			else if (att1->attbyval)
-			{
-				result = (values1[i1] == values2[i2]);
-			}
-			else
-			{
-				result = (memcmp(DatumGetPointer(values1[i1]),
-								 DatumGetPointer(values2[i2]),
-								 att1->attlen) == 0);
-			}
+			result = datum_image_eq(values1[i1], values2[i2], att1->attbyval, att2->attlen);
 			if (!result)
 				break;
 		}
diff --git a/src/include/utils/datum.h b/src/include/utils/datum.h
index 7b913578ab..4365bf06e6 100644
--- a/src/include/utils/datum.h
+++ b/src/include/utils/datum.h
@@ -46,6 +46,15 @@ extern Datum datumTransfer(Datum value, bool typByVal, int typLen);
 extern bool datumIsEqual(Datum value1, Datum value2,
 			 bool typByVal, int typLen);
 
+/*
+ * datum_image_eq
+ *
+ * Compares two datums for identical contents, based on byte images.  Return
+ * true if the two datums are equal, false otherwise.
+ */
+extern bool datum_image_eq(Datum value1, Datum value2,
+						   bool typByVal, int typLen);
+
 /*
  * Serialize and restore datums so that we can transfer them to parallel
  * workers.
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index f1a664e339..401514a3e0 100644
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -1494,6 +1494,40 @@ delete from pktable2 where f1 = 1;
 alter table fktable2 drop constraint fktable2_f1_fkey;
 ERROR:  cannot ALTER TABLE "pktable2" because it has pending trigger events
 commit;
+drop table pktable2, fktable2;
+--
+-- Test keys that "look" different but compare as equal
+--
+create table pktable2 (a float8, b float8, primary key (a, b));
+create table fktable2 (x float8, y float8, foreign key (x, y) references pktable2 (a, b) on update cascade);
+insert into pktable2 values ('-0', '-0');
+insert into fktable2 values ('-0', '-0');
+select * from pktable2;
+ a  | b  
+----+----
+ -0 | -0
+(1 row)
+
+select * from fktable2;
+ x  | y  
+----+----
+ -0 | -0
+(1 row)
+
+update pktable2 set a = '0' where a = '-0';
+select * from pktable2;
+ a | b  
+---+----
+ 0 | -0
+(1 row)
+
+-- should have updated fktable2.x
+select * from fktable2;
+ x | y  
+---+----
+ 0 | -0
+(1 row)
+
 drop table pktable2, fktable2;
 --
 -- Foreign keys and partitioned tables
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 4639fb4509..beeaf3277d 100644
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -1120,6 +1120,26 @@ commit;
 
 drop table pktable2, fktable2;
 
+--
+-- Test keys that "look" different but compare as equal
+--
+create table pktable2 (a float8, b float8, primary key (a, b));
+create table fktable2 (x float8, y float8, foreign key (x, y) references pktable2 (a, b) on update cascade);
+
+insert into pktable2 values ('-0', '-0');
+insert into fktable2 values ('-0', '-0');
+
+select * from pktable2;
+select * from fktable2;
+
+update pktable2 set a = '0' where a = '-0';
+
+select * from pktable2;
+-- should have updated fktable2.x
+select * from fktable2;
+
+drop table pktable2, fktable2;
+
 
 --
 -- Foreign keys and partitioned tables