diff --git a/gcc/testsuite/lib/g++-dg.exp b/gcc/testsuite/lib/g++-dg.exp
index a1bc37074b57d27d5d536f0a129ea52b823dde1b..59e8081a29dd59ecf6d8505669d6824b4e03b19d 100644
--- a/gcc/testsuite/lib/g++-dg.exp
+++ b/gcc/testsuite/lib/g++-dg.exp
@@ -27,8 +27,8 @@ proc g++-dg-prune { system text } {
     return [gcc-dg-prune $system $text]
 }
 
-# Modified dg-runtest that runs tests in both C++98 and C++11 modes
-# unless they specifically specify one or the other.
+# Modified dg-runtest that runs tests in multiple standard modes,
+# unless they specifically specify one standard.
 proc g++-dg-runtest { testcases flags default-extra-flags } {
     global runtests
 
@@ -39,7 +39,7 @@ proc g++-dg-runtest { testcases flags default-extra-flags } {
 	}
 
 	# If the testcase specifies a standard, use that one.
-	# If not, run it under both standards, allowing GNU extensions
+	# If not, run it under several standards, allowing GNU extensions
 	# if there's a dg-options line.
 	if ![search_for $test "-std=*++"] {
 	    if [search_for $test "dg-options"] {
@@ -48,6 +48,7 @@ proc g++-dg-runtest { testcases flags default-extra-flags } {
 		set std_prefix "-std=c++"
 	    }
 
+	    # See g++.exp for the initial value of this list.
 	    global gpp_std_list
 	    if { [llength $gpp_std_list] > 0 } {
 		set std_list $gpp_std_list
diff --git a/gcc/testsuite/lib/g++.exp b/gcc/testsuite/lib/g++.exp
index 3744ebe4b447628fcb1d88c1955a96ae81581df4..24ef068b2395361759deb654281e22a9abbf9729 100644
--- a/gcc/testsuite/lib/g++.exp
+++ b/gcc/testsuite/lib/g++.exp
@@ -32,7 +32,11 @@ load_lib target-libpath.exp
 
 
 set gpp_compile_options ""
-set gpp_std_list { }
+# Allow gpp_std_list to be set in configuration files, e.g., ~/.dejagnurc
+if ![info exists gpp_std_list] {
+    set gpp_std_list { }
+}
+# Allow gpp_std_list to be set from the environment.
 if [info exists env(GXX_TESTSUITE_STDS)] {
     set gpp_std_list [split $env(GXX_TESTSUITE_STDS) ","]
 }