diff --git a/gcc/config/s390/driver-native.c b/gcc/config/s390/driver-native.c
index 5f7fe0a..08ec85e 100644
--- a/gcc/config/s390/driver-native.c
+++ b/gcc/config/s390/driver-native.c
@@ -84,9 +84,8 @@ s390_host_detect_local_cpu (int argc, const char **argv)
 	  machine_id = strtol (p, NULL, 16);
 	  switch (machine_id)
 	    {
+	      /* g5 and g6 default to z900 */
 	    case 0x9672:
-	      cpu = "g5";
-	      break;
 	    case 0x2064:
 	    case 0x2066:
 	      cpu = "z900";
diff --git a/gcc/config/s390/s390.c b/gcc/config/s390/s390.c
index bc6f05b..2a42818 100644
--- a/gcc/config/s390/s390.c
+++ b/gcc/config/s390/s390.c
@@ -13569,9 +13569,27 @@ s390_function_specific_restore (struct gcc_options *opts,
 }
 
 static void
-s390_option_override_internal (struct gcc_options *opts,
+s390_option_override_internal (bool main_args_p,
+			       struct gcc_options *opts,
 			       const struct gcc_options *opts_set)
 {
+  const char *prefix;
+  const char *suffix;
+
+  /* Set up prefix/suffix so the error messages refer to either the command
+     line argument, or the attribute(target).  */
+  if (main_args_p)
+    {
+      prefix = "-m";
+      suffix = "";
+    }
+  else
+    {
+      prefix = "option(\"";
+      suffix = "\")";
+    }
+
+
   /* Architecture mode defaults according to ABI.  */
   if (!(opts_set->x_target_flags & MASK_ZARCH))
     {
@@ -13583,13 +13601,26 @@ s390_option_override_internal (struct gcc_options *opts,
 
   /* Set the march default in case it hasn't been specified on cmdline.  */
   if (!opts_set->x_s390_arch)
-    opts->x_s390_arch = TARGET_ZARCH_P (opts->x_target_flags)
-      ? PROCESSOR_2064_Z900 : PROCESSOR_9672_G5;
+    opts->x_s390_arch = PROCESSOR_2064_Z900;
+  else if (opts->x_s390_arch == PROCESSOR_9672_G5
+	   || opts->x_s390_arch == PROCESSOR_9672_G6)
+    warning (OPT_Wdeprecated, "%sarch=%s%s is deprecated and will be removed "
+	     "in future releases; use at least %sarch=z900%s",
+	     prefix, opts->x_s390_arch == PROCESSOR_9672_G5 ? "g5" : "g6",
+	     suffix, prefix, suffix);
+
   opts->x_s390_arch_flags = processor_flags_table[(int) opts->x_s390_arch];
 
   /* Determine processor to tune for.  */
   if (!opts_set->x_s390_tune)
     opts->x_s390_tune = opts->x_s390_arch;
+  else if (opts->x_s390_tune == PROCESSOR_9672_G5
+	   || opts->x_s390_tune == PROCESSOR_9672_G6)
+    warning (OPT_Wdeprecated, "%stune=%s%s is deprecated and will be removed "
+	     "in future releases; use at least %stune=z900%s",
+	     prefix, opts->x_s390_tune == PROCESSOR_9672_G5 ? "g5" : "g6",
+	     suffix, prefix, suffix);
+
   opts->x_s390_tune_flags = processor_flags_table[opts->x_s390_tune];
 
   /* Sanity checks.  */
@@ -13800,7 +13831,7 @@ s390_option_override (void)
   /* Set up function hooks.  */
   init_machine_status = s390_init_machine_status;
 
-  s390_option_override_internal (&global_options, &global_options_set);
+  s390_option_override_internal (true, &global_options, &global_options_set);
 
   /* Save the initial options in case the user does function specific
      options.  */
@@ -14102,7 +14133,7 @@ s390_valid_target_attribute_tree (tree args,
 	dest[i] |= src[i];
 
       /* Do any overrides, such as arch=xxx, or tune=xxx support.  */
-      s390_option_override_internal (opts, &new_opts_set);
+      s390_option_override_internal (false, opts, &new_opts_set);
       /* Save the current options unless we are validating options for
 	 #pragma.  */
       t = build_target_option_node (opts);
diff --git a/gcc/config/s390/s390.h b/gcc/config/s390/s390.h
index 52ed7a4..603e638 100644
--- a/gcc/config/s390/s390.h
+++ b/gcc/config/s390/s390.h
@@ -214,7 +214,7 @@ extern const char *s390_host_detect_local_cpu (int argc, const char **argv);
   MARCH_MTUNE_NATIVE_SPECS,					\
   "%{!m31:%{!m64:-m" S390_TARGET_BITS_STRING "}}",		\
   "%{!mesa:%{!mzarch:%{m31:-mesa}%{m64:-mzarch}}}",		\
-  "%{!march=*:%{mesa:-march=g5}%{mzarch:-march=z900}}"
+  "%{!march=*:-march=z900}"
 
 /* Constants needed to control the TEST DATA CLASS (TDC) instruction.  */
 #define S390_TDC_POSITIVE_ZERO                     (1 << 11)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 9b3e2fe..346e40b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -20893,14 +20893,12 @@ The default is to not print debug information.
 
 @item -march=@var{cpu-type}
 @opindex march
-Generate code that runs on @var{cpu-type}, which is the name of a system
-representing a certain processor type.  Possible values for
-@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
-@samp{z9-109}, @samp{z9-ec}, @samp{z10},  @samp{z196}, @samp{zEC12},
-and @samp{z13}.
-When generating code using the instructions available on z/Architecture,
-the default is @option{-march=z900}.  Otherwise, the default is
-@option{-march=g5}.
+Generate code that runs on @var{cpu-type}, which is the name of a
+system representing a certain processor type.  Possible values for
+@var{cpu-type} are @samp{z900}, @samp{z990}, @samp{z9-109},
+@samp{z9-ec}, @samp{z10}, @samp{z196}, @samp{zEC12}, and @samp{z13}.
+The default is @option{-march=z900}.  @samp{g5} and @samp{g6} are
+deprecated and will be removed with future releases.
 
 @item -mtune=@var{cpu-type}
 @opindex mtune
diff --git a/gcc/testsuite/gcc.target/s390/hotpatch-8.c b/gcc/testsuite/gcc.target/s390/hotpatch-8.c
index 1ea3160..c5b71a5 100644
--- a/gcc/testsuite/gcc.target/s390/hotpatch-8.c
+++ b/gcc/testsuite/gcc.target/s390/hotpatch-8.c
@@ -1,7 +1,7 @@
 /* Functional tests for the function hotpatching feature.  */
 
 /* { dg-do compile { target { ! lp64 } } } */
-/* { dg-options "-mesa -march=g5 -mhotpatch=0,3" } */
+/* { dg-options "-mesa -march=g5 -Wno-deprecated -mhotpatch=0,3" } */
 
 #include <stdio.h>
 
diff --git a/gcc/testsuite/gcc.target/s390/hotpatch-9.c b/gcc/testsuite/gcc.target/s390/hotpatch-9.c
index e30f276..9ccc8fd 100644
--- a/gcc/testsuite/gcc.target/s390/hotpatch-9.c
+++ b/gcc/testsuite/gcc.target/s390/hotpatch-9.c
@@ -1,7 +1,7 @@
 /* Functional tests for the function hotpatching feature.  */
 
 /* { dg-do compile { target { ! lp64 } } } */
-/* { dg-options "-mesa -march=g5 -mhotpatch=0,4" } */
+/* { dg-options "-mesa -march=g5 -Wno-deprecated -mhotpatch=0,4" } */
 
 #include <stdio.h>
 
