diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index cdeedb1db91..4e62a06e0c9 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,9 +1,17 @@
 2015-12-02  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
 
-        * gcc.dg/builtin-bswap-6a.c: Add -march=z900 for s390 and s390x in
+	* gcc.dg/optimize-bswapdi-1.c: Force using -mzarch on s390 and
+	s390x to enable 64 bit bswap patterns.
+	* gcc.dg/optimize-bswapdi-2.c: Likewise.
+	* gcc.dg/optimize-bswapdi-3.c: Likewise.
+	* lib/target-supports.exp: Add a comment for s390.
+
+2015-12-02  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
+
+	* gcc.dg/builtin-bswap-6a.c: Add -march=z900 for s390 and s390x in
 	order to make -m31 work.
-        * gcc.dg/optimize-bswapsi-1.c: Likewise.
-        * gcc.dg/optimize-bswapsi-2.c: Likewise.
+	* gcc.dg/optimize-bswapsi-1.c: Likewise.
+	* gcc.dg/optimize-bswapsi-2.c: Likewise.
 
 2015-12-02  Jakub Jelinek  <jakub@redhat.com>
 
@@ -306,7 +314,7 @@
 
 2015-11-30  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
 
-        * gcc.target/s390/load-relative-check.c: Add -mzarch.
+	* gcc.target/s390/load-relative-check.c: Add -mzarch.
 
 2015-11-30  Eric Botcazou  <ebotcazou@adacore.com>
 
diff --git a/gcc/testsuite/gcc.dg/optimize-bswapdi-1.c b/gcc/testsuite/gcc.dg/optimize-bswapdi-1.c
index 0b5fe29687a..251dbc2da95 100644
--- a/gcc/testsuite/gcc.dg/optimize-bswapdi-1.c
+++ b/gcc/testsuite/gcc.dg/optimize-bswapdi-1.c
@@ -2,6 +2,7 @@
 /* { dg-require-effective-target bswap64 } */
 /* { dg-require-effective-target stdint_types } */
 /* { dg-options "-O2 -fdump-tree-bswap" } */
+/* { dg-additional-options "-mzarch" { target s390*-*-* } } */
 
 #include <stdint.h>
 #define __const_swab64(x) ((uint64_t)(			                        \
diff --git a/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c b/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c
index 7ac0323825a..2c8108707dc 100644
--- a/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c
+++ b/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c
@@ -2,6 +2,7 @@
 /* { dg-require-effective-target bswap64 } */
 /* { dg-require-effective-target stdint_types } */
 /* { dg-options "-O2 -fdump-tree-bswap" } */
+/* { dg-additional-options "-mzarch" { target s390*-*-* } } */
 
 #include <stdint.h>
 
diff --git a/gcc/testsuite/gcc.dg/optimize-bswapdi-3.c b/gcc/testsuite/gcc.dg/optimize-bswapdi-3.c
index 3c66505a64f..273b4bc622c 100644
--- a/gcc/testsuite/gcc.dg/optimize-bswapdi-3.c
+++ b/gcc/testsuite/gcc.dg/optimize-bswapdi-3.c
@@ -2,6 +2,7 @@
 /* { dg-require-effective-target bswap64 } */
 /* { dg-require-effective-target stdint_types } */
 /* { dg-options "-O2 -fdump-tree-bswap" } */
+/* { dg-additional-options "-mzarch" { target s390*-*-* } } */
 
 #include <stdint.h>
 
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 2275fd3f44c..e3b30f1551c 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -5543,6 +5543,8 @@ proc check_effective_target_bswap32 { } {
 }
 
 # Return 1 if the target supports 64-bit byte swap instructions.
+#
+# Note: 32bit s390 targets require -mzarch in dg-options.
 
 proc check_effective_target_bswap64 { } {
     global et_bswap64_saved