diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 432cdccd2c..92847f7217 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2017-03-08  Pedro Alves  <palves@redhat.com>
+
+	PR cli/21218
+	* top.c (gdb_readline_wrapper): Avoid passing NULL to
+	display_gdb_prompt.
+	(command_line_input): Add comment.
+
 2017-03-08  Pedro Alves  <palves@redhat.com>
 
 	PR tui/21216
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 0654bef40d..d7b603b43f 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2017-03-08  Pedro Alves  <palves@redhat.com>
+	    Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	PR cli/21218
+	* gdb.base/commands.exp (backslash_in_multi_line_command_test):
+	New proc.
+	(top level): Call it.
+
 2017-03-08  Pedro Alves  <palves@redhat.com>
 
 	PR tui/21216
diff --git a/gdb/testsuite/gdb.base/commands.exp b/gdb/testsuite/gdb.base/commands.exp
index 9ad70f5244..6d3c398c6e 100644
--- a/gdb/testsuite/gdb.base/commands.exp
+++ b/gdb/testsuite/gdb.base/commands.exp
@@ -1003,6 +1003,34 @@ proc_with_prefix redefine_backtrace_test {} {
     gdb_test "bt" "hibob" "execute bt command"
 }
 
+# Test an input line split with a continuation character (backslash)
+# while entering a multi-line command (in a secondary prompt).
+
+proc_with_prefix backslash_in_multi_line_command_test {} {
+    gdb_breakpoint "main"
+
+    gdb_test_multiple "commands" "commands" {
+	-re "End with a line saying just \"end\"\\.\r\n>$" {
+	    pass "commands"
+	}
+    }
+
+    set test "input line split with backslash"
+    send_gdb "print \\\nargc\n"
+    gdb_test_multiple "" $test {
+	-re "^print \\\\\r\nargc\r\n>$" {
+	    pass $test
+	}
+    }
+
+    gdb_test_no_output "end"
+
+    # Input any command, just to be sure the readline state is sane.
+    # In PR 21218, this would trigger the infamous:
+    # readline: readline_callback_read_char() called with no handler!
+    gdb_test "print 1" "" "run command"
+}
+
 gdbvar_simple_if_test
 gdbvar_simple_while_test
 gdbvar_complex_if_while_test
@@ -1027,5 +1055,6 @@ recursive_source_test
 if_commands_test
 error_clears_commands_left
 redefine_hook_test
+backslash_in_multi_line_command_test
 # This one should come last, as it redefines "backtrace".
 redefine_backtrace_test
diff --git a/gdb/top.c b/gdb/top.c
index 6bf9d8c021..295b6806de 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1030,8 +1030,11 @@ gdb_readline_wrapper (const char *prompt)
   if (cleanup->target_is_async_orig)
     target_async (0);
 
-  /* Display our prompt and prevent double prompt display.  */
-  display_gdb_prompt (prompt);
+  /* Display our prompt and prevent double prompt display.  Don't pass
+     down a NULL prompt, since that has special meaning for
+     display_gdb_prompt -- it indicates a request to print the primary
+     prompt, while we want a secondary prompt here.  */
+  display_gdb_prompt (prompt != NULL ? prompt : "");
   if (ui->command_editing)
     rl_already_prompted = 1;
 
@@ -1307,6 +1310,9 @@ command_line_input (const char *prompt_arg, int repeat, char *annotation_suffix)
       if (cmd != NULL)
 	break;
 
+      /* Got partial input.  I.e., got a line that ends with a
+	 continuation character (backslash).  Suppress printing the
+	 prompt again.  */
       prompt = NULL;
     }