diff --git a/gas/ChangeLog b/gas/ChangeLog
index adeb38bb27..dd61142231 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,23 @@
+2017-08-11  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR gas/21667
+	* read.c (pseudo_set): Update error message for alias of common
+	symbol.
+	* write.c (write_object_file): Disallow both local and global
+	aliases of common symbol.
+	* testsuite/gas/elf/common5a.d: New file.
+	* testsuite/gas/elf/common5a.l: Likewise.
+	* testsuite/gas/elf/common5a.s: Likewise.
+	* testsuite/gas/elf/common5b.d: Likewise.
+	* testsuite/gas/elf/common5b.l: Likewise.
+	* testsuite/gas/elf/common5b.s: Likewise.
+	* testsuite/gas/elf/common5c.d: Likewise.
+	* testsuite/gas/elf/common5c.s: Likewise.
+	* testsuite/gas/elf/common5d.d: Likewise.
+	* testsuite/gas/elf/common5d.s: Likewise.
+	* testsuite/gas/elf/elf.exp: Run common5a, common5b, common5c
+	and common5d.
+
 2017-08-10  Nick Clifton  <nickc@redhat.com>
 
 	PR gas/21939
diff --git a/gas/read.c b/gas/read.c
index 9627ef513b..0b0b05803c 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -3870,7 +3870,7 @@ pseudo_set (symbolS *symbolP)
 	  symbolS *s = exp.X_add_symbol;
 
 	  if (S_IS_COMMON (s))
-	    as_bad (_("`%s' can't be equated to common symbol '%s'"),
+	    as_bad (_("`%s' can't be equated to common symbol `%s'"),
 		    S_GET_NAME (symbolP), S_GET_NAME (s));
 
 	  S_SET_SEGMENT (symbolP, seg);
diff --git a/gas/testsuite/gas/elf/common5a.d b/gas/testsuite/gas/elf/common5a.d
new file mode 100644
index 0000000000..9c790e61af
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5a.d
@@ -0,0 +1,5 @@
+#source: common5a.s
+#as: 
+#error-output: common5a.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.
diff --git a/gas/testsuite/gas/elf/common5a.l b/gas/testsuite/gas/elf/common5a.l
new file mode 100644
index 0000000000..7574dc6a65
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5a.l
@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+[^:]*: Error: `foo1' can't be equated to common symbol `foo'
diff --git a/gas/testsuite/gas/elf/common5a.s b/gas/testsuite/gas/elf/common5a.s
new file mode 100644
index 0000000000..d4b0acf36d
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5a.s
@@ -0,0 +1,3 @@
+	.set	foo1,foo
+	.globl	foo1
+	.comm	foo,8,8
diff --git a/gas/testsuite/gas/elf/common5b.d b/gas/testsuite/gas/elf/common5b.d
new file mode 100644
index 0000000000..b1dabdcb66
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5b.d
@@ -0,0 +1,5 @@
+#source: common5b.s
+#as: 
+#error-output: common5b.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.
diff --git a/gas/testsuite/gas/elf/common5b.l b/gas/testsuite/gas/elf/common5b.l
new file mode 100644
index 0000000000..171bed0693
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5b.l
@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+[^:]*:2: Error: `foo1' can't be equated to common symbol `foo'
diff --git a/gas/testsuite/gas/elf/common5b.s b/gas/testsuite/gas/elf/common5b.s
new file mode 100644
index 0000000000..df79fcbca8
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5b.s
@@ -0,0 +1,3 @@
+	.comm	foo,8,8
+	.set	foo1,foo
+	.globl	foo1
diff --git a/gas/testsuite/gas/elf/common5c.d b/gas/testsuite/gas/elf/common5c.d
new file mode 100644
index 0000000000..1e106ad2e3
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5c.d
@@ -0,0 +1,5 @@
+#source: common5c.s
+#as: 
+#error-output: common5a.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.
diff --git a/gas/testsuite/gas/elf/common5c.s b/gas/testsuite/gas/elf/common5c.s
new file mode 100644
index 0000000000..fa9db8d584
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5c.s
@@ -0,0 +1,2 @@
+	.set	foo1,foo
+	.comm	foo,8,8
diff --git a/gas/testsuite/gas/elf/common5d.d b/gas/testsuite/gas/elf/common5d.d
new file mode 100644
index 0000000000..9f51636dbe
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5d.d
@@ -0,0 +1,5 @@
+#source: common5d.s
+#as: 
+#error-output: common5b.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.
diff --git a/gas/testsuite/gas/elf/common5d.s b/gas/testsuite/gas/elf/common5d.s
new file mode 100644
index 0000000000..6da5cb3bfe
--- /dev/null
+++ b/gas/testsuite/gas/elf/common5d.s
@@ -0,0 +1,2 @@
+	.comm	foo,8,8
+	.set	foo1,foo
diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index 1284619dc2..6737486296 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -252,6 +252,10 @@ if { [is_elf_format] } then {
 	run_dump_test "common3b"
 	run_dump_test "common4a"
 	run_dump_test "common4b"
+	run_dump_test "common5a"
+	run_dump_test "common5b"
+	run_dump_test "common5c"
+	run_dump_test "common5d"
     }
 
     run_dump_test "strtab"
diff --git a/gas/write.c b/gas/write.c
index 8efdbc506f..4f6547dfb8 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -2107,12 +2107,11 @@ write_object_file (void)
 
 	      if (S_IS_COMMON (symp)
 		  && !TC_FAKE_LABEL (sname)
-		  && !S_IS_WEAKREFR (symp)
-		  && (!S_IS_EXTERNAL (symp) || S_IS_LOCAL (symp)))
+		  && !S_IS_WEAKREFR (symp))
 		{
 		  expressionS *e = symbol_get_value_expression (symp);
 
-		  as_bad (_("Local symbol `%s' can't be equated to common symbol `%s'"),
+		  as_bad (_("`%s' can't be equated to common symbol `%s'"),
 			  sname, S_GET_NAME (e->X_add_symbol));
 		}
 	      if (S_GET_SEGMENT (symp) == reg_section)