diff --git a/gdb/cp-namespace.c b/gdb/cp-namespace.c
index 72002d6..016a42f 100644
--- a/gdb/cp-namespace.c
+++ b/gdb/cp-namespace.c
@@ -170,7 +170,7 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
      ':' may be in the args of a template spec.  This isn't intended to be
      a complete test, just cheap and documentary.  */
   if (strchr (name, '<') == NULL && strchr (name, '(') == NULL)
-    gdb_assert (strchr (name, ':') == NULL);
+    gdb_assert (strstr (name, "::") == NULL);
 
   sym = lookup_symbol_in_static_block (name, block, domain);
   if (sym.symbol != NULL)
@@ -246,10 +246,9 @@ cp_search_static_and_baseclasses (const char *name,
   struct block_symbol klass_sym;
   struct type *klass_type;
 
-  /* The test here uses <= instead of < because Fortran also uses this,
-     and the module.exp testcase will pass "modmany::" for NAME here.  */
-  gdb_assert (prefix_len + 2 <= strlen (name));
-  gdb_assert (name[prefix_len + 1] == ':');
+  /* Check for malformed input.  */
+  if (prefix_len + 2 > strlen (name) || name[prefix_len + 1] != ':')
+    return null_block_symbol;
 
   /* Find the name of the class and the name of the method, variable, etc.  */
 
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index df127c4..a71c6ad 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -1037,8 +1037,13 @@ cp_find_first_component_aux (const char *name, int permissive)
 	      return strlen (name);
 	    }
 	case '\0':
-	case ':':
 	  return index;
+	case ':':
+	  /* ':' marks a component iff the next character is also a ':'.
+	     Otherwise it is probably malformed input.  */
+	  if (name[index + 1] == ':')
+	    return index;
+	  break;
 	case 'o':
 	  /* Operator names can screw up the recursion.  */
 	  if (operator_possible
diff --git a/gdb/testsuite/gdb.cp/scope-err.cc b/gdb/testsuite/gdb.cp/scope-err.cc
new file mode 100644
index 0000000..19c92d8
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/scope-err.cc
@@ -0,0 +1,35 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+myfunction (int aa)
+{
+  int i;
+
+  i = aa + 42;
+  return i;    /* set breakpoint here */
+}
+
+int
+main (void)
+{
+  int a;
+
+  a = myfunction (a);
+
+  return a;
+}
diff --git a/gdb/testsuite/gdb.linespec/ls-errs-cp.cc b/gdb/testsuite/gdb.linespec/ls-errs-cp.cc
new file mode 100644
index 0000000..a3a43db
--- /dev/null
+++ b/gdb/testsuite/gdb.linespec/ls-errs-cp.cc
@@ -0,0 +1,36 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2012-2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+myfunction (int aa)
+{
+  int i;
+
+  i = aa + 42;
+  return i;    /* set breakpoint here */
+}
+
+int
+main (void)
+{
+  int a;
+
+  a = myfunction (a);
+
+ here:
+  return a;
+}
diff --git a/gdb/testsuite/gdb.linespec/ls-errs-cp.exp b/gdb/testsuite/gdb.linespec/ls-errs-cp.exp
new file mode 100644
index 0000000..be1c3ba
--- /dev/null
+++ b/gdb/testsuite/gdb.linespec/ls-errs-cp.exp
@@ -0,0 +1,240 @@
+# Copyright 2012-2016 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Tests for linespec errors with C++.
+# Derived from gdb.linespec/ls-errs.exp.
+
+if { [skip_cplus_tests] } { continue }
+
+standard_testfile .cc
+set exefile $testfile
+
+if {[prepare_for_testing $testfile $exefile $srcfile {debug c++}]} {
+    return -1
+}
+
+# Turn off the pending breakpoint queries.
+gdb_test_no_output "set breakpoint pending off"
+
+# Turn off completion limiting
+gdb_test_no_output "set max-completions unlimited"
+
+if ![runto_main] {
+    fail "Can't run to main"
+    return 0
+}
+
+# Run to a location in the file.
+set bp_location [gdb_get_line_number "set breakpoint here"]
+
+gdb_test "break $srcfile:$bp_location" \
+    "Breakpoint.*at.* file .*$srcfile, line $bp_location\\." \
+    "breakpoint line number in file"
+
+gdb_continue_to_breakpoint "$bp_location"
+
+# We intentionally do not use gdb_breakpoint for these tests.
+
+# Break at 'linespec' and expect the message in ::error_messages indexed by
+# msg_id with the associated args.
+proc test_break {linespec msg_id args} {
+    global error_messages
+
+    gdb_test "break $linespec" [string_to_regexp \
+				[eval format \$error_messages($msg_id) $args]]
+}
+
+# Common error message format strings.
+array set error_messages {
+    invalid_file "No source file named %s."
+    invalid_function "Function \"%s\" not defined."
+    invalid_var_or_func "Undefined convenience variable or function \"%s\" not defined."
+    invalid_function_f "Function \"%s\" not defined in \"%s\"."
+    invalid_var_or_func_f \
+	"Undefined convenience variable or function \"%s\" not defined in \"%s\"."
+    invalid_label "No label \"%s\" defined in function \"%s\"."
+    invalid_parm "invalid linespec argument, \"%s\""
+    invalid_offset "No line %d in the current file."
+    invalid_offset_f "No line %d in file \"%s\"."
+    malformed_line_offset "malformed line offset: \"%s\""
+    source_incomplete \
+	"Source filename requires function, label, or line offset."
+    unexpected "malformed linespec error: unexpected %s"
+    unexpected_opt "malformed linespec error: unexpected %s, \"%s\""
+    unmatched_quote "unmatched quote"
+    garbage "Garbage '%s' at end of command"
+}
+
+# Some commonly used whitespace tests around ':'.
+set spaces [list ":" ": " " :" " : " "\t:  " "  :\t" "\t:\t" " \t:\t " \
+		"\t  \t:\t  \t  \t"]
+
+# A list of invalid offsets.
+set invalid_offsets [list -100 +500 1000]
+
+# Try some simple, invalid linespecs involving spaces.
+foreach x $spaces {
+    test_break $x unexpected "colon"
+}
+
+# Test invalid filespecs starting with offset.  This is done
+# first so that default offsets are tested.
+foreach x $invalid_offsets {
+    set offset $x
+
+    # Relative offsets are relative to line 16.  Adjust
+    # expected offset from error message accordingly.
+    if {[string index $x 0] == "+" ||
+	[string index $x 0] == "-"} {
+	incr offset 24
+    }
+    test_break $x invalid_offset $offset
+    test_break "-line $x" invalid_offset $offset
+}
+
+# Test offsets with trailing tokens w/ and w/o spaces.
+foreach x $spaces {
+    test_break "3$x" unexpected "colon"
+    test_break "+10$x" unexpected "colon"
+    test_break "-10$x" unexpected "colon"
+}
+
+foreach x {1 +1 +100 -10} {
+    test_break "3 $x" unexpected_opt "number" $x
+    test_break "-line 3 $x" garbage $x
+    test_break "+10 $x" unexpected_opt "number" $x
+    test_break "-line +10 $x" garbage $x
+    test_break "-10 $x" unexpected_opt "number" $x
+    test_break "-line -10 $x" garbage $x
+}
+
+foreach x {3 +10 -10} {
+    test_break "$x foo" unexpected_opt "string" "foo"
+    test_break "-line $x foo" garbage "foo"
+}
+
+# Test invalid linespecs starting with filename.
+set invalid_files [list "this_file_doesn't_exist.cc" \
+		   "this file has spaces.cc" \
+	           "\"file::colons.cc\"" \
+	           "'file::colons.cc'" \
+	           "\"this \"file\" has quotes.cc\"" \
+	           "'this \"file\" has quotes.cc'" \
+	           "'this 'file' has quotes.cc'" \
+	           "\"this 'file' has quotes.cc\"" \
+	           "\"spaces: and :colons.cc\"" \
+	           "'more: :spaces: :and  colons::.cc'" \
+		   "C:/nonexist-with-windrive.cc"]
+
+foreach x $invalid_files {
+    # Remove any quoting from FILENAME for the error message.
+    test_break "$x:3" invalid_file [string trim $x \"']
+}
+foreach x [list "this_file_doesn't_exist.cc" \
+	       "file::colons.cc" \
+	       "'file::colons.cc'"] {
+    test_break "-source $x -line 3" \
+	invalid_file [string trim $x \"']
+}
+
+# Test that option lexing stops at whitespace boundaries
+test_break "-source this file has spaces.cc -line 3" \
+    invalid_file "this"
+
+test_break "-function function whitespace" \
+    invalid_function "function"
+
+test_break "-source $srcfile -function function whitespace" \
+    invalid_function_f "function" $srcfile
+
+test_break "-function main -label label whitespace" \
+    invalid_label "label" "main"
+
+# Test unmatched quotes.
+foreach x {"\"src-file.cc'" "'src-file.cc"} {
+    test_break "$x:3" unmatched_quote
+}
+
+test_break $srcfile invalid_function $srcfile
+foreach x {"foo" " foo" " foo "} {
+    # Trim any leading/trailing whitespace for error messages.
+    test_break "$srcfile:$x" invalid_function_f [string trim $x] $srcfile
+    test_break "-source $srcfile -function $x" \
+	invalid_function_f [string trim $x] $srcfile
+    test_break "$srcfile:main:$x" invalid_label [string trim $x] "main"
+    test_break "-source $srcfile -function main -label $x" \
+	invalid_label [string trim $x] "main"
+}
+
+foreach x $spaces {
+    test_break "$srcfile$x" unexpected "end of input"
+    test_break "$srcfile:main$x" unexpected "end of input"
+}
+
+test_break "${srcfile}::" invalid_function "${srcfile}::"
+test_break "$srcfile:3 1" unexpected_opt "number" "1"
+test_break "-source $srcfile -line 3 1" garbage "1"
+test_break "$srcfile:3 +100" unexpected_opt "number" "+100"
+test_break "-source $srcfile -line 3 +100" garbage "+100"
+test_break "$srcfile:3 -100" unexpected_opt "number" "-100"
+test_break "$srcfile:3 foo" unexpected_opt "string" "foo"
+test_break "-source $srcfile -line 3 foo" garbage "foo"
+
+foreach x $invalid_offsets {
+    test_break "$srcfile:$x" invalid_offset_f $x $srcfile
+    test_break "\"$srcfile:$x\"" invalid_offset_f $x $srcfile
+    test_break "'$srcfile:$x'" invalid_offset_f $x $srcfile
+    test_break "-source $srcfile -line $x" invalid_offset_f $x $srcfile
+}
+test_break "-source $srcfile -line -x" malformed_line_offset "-x"
+
+# Test invalid filespecs starting with function.
+foreach x {"foobar" "foo::bar" "foo.bar" "foo ." "foo bar" "foo 1" \
+	       "foo 0" "foo +10" "foo -10" "foo +100" "foo -100"} {
+    test_break $x invalid_function $x
+    test_break "-function \"$x\"" invalid_function $x
+}
+
+foreach x $spaces {
+    test_break "main${x}there" invalid_label "there" "main"
+    if {[test_compiler_info {clang-*-*}]} {  setup_xfail clang/14500 *-*-* }
+    test_break "main:here${x}" unexpected "end of input"
+}
+
+foreach x {"3" "+100" "-100" "foo"} {
+    test_break "main 3" invalid_function "main 3"
+    test_break "-function \"main $x\"" invalid_function "main $x"
+    test_break "main:here $x" invalid_label "here $x" "main"
+    test_break "-function main -label \"here $x\"" \
+	invalid_label "here $x" "main"
+}
+
+foreach x {"if" "task" "thread"} {
+    test_break $x invalid_function $x
+}
+
+test_break "'main.cc'flubber" unexpected_opt "string" "flubber"
+test_break "'main.cc',21" invalid_function "main.cc"
+test_break "'main.cc' " invalid_function "main.cc"
+test_break "'main.cc'3" unexpected_opt "number" "3"
+test_break "'main.cc'+3" unexpected_opt "number" "+3"
+
+# Test undefined convenience variables.
+set x {$zippo}
+test_break $x invalid_var_or_func $x
+test_break "$srcfile:$x" invalid_var_or_func_f $x $srcfile
+
+# Explicit linespec-specific tests
+test_break "-source $srcfile" source_incomplete
diff --git a/gdb/testsuite/gdb.mi/mi-linespec-err-cp.cc b/gdb/testsuite/gdb.mi/mi-linespec-err-cp.cc
new file mode 100644
index 0000000..19c92d8
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-linespec-err-cp.cc
@@ -0,0 +1,35 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+myfunction (int aa)
+{
+  int i;
+
+  i = aa + 42;
+  return i;    /* set breakpoint here */
+}
+
+int
+main (void)
+{
+  int a;
+
+  a = myfunction (a);
+
+  return a;
+}
diff --git a/gdb/testsuite/gdb.mi/mi-linespec-err-cp.exp b/gdb/testsuite/gdb.mi/mi-linespec-err-cp.exp
new file mode 100644
index 0000000..1a8682e
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-linespec-err-cp.exp
@@ -0,0 +1,57 @@
+# Copyright 2016 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Regression test for PR breakpoints/18303.  Tests that the correct
+# errors is generated when setting a breakpoint in a non-existent
+# file with a Windows-style logical drive names and C++.
+
+if { [skip_cplus_tests] } { continue }
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+standard_testfile .cc
+set exefile $testfile
+
+if {[prepare_for_testing $testfile $exefile $srcfile {debug c++}]} {
+    return -1
+}
+
+gdb_exit
+if [mi_gdb_start] {
+    continue
+}
+
+# Turn off the pending breakpoint queries.
+mi_gdb_test "-interpreter-exec console \"set breakpoint pending off\"" \
+  {=cmd-param-changed,param=\"breakpoint pending\",.*\^done} \
+  "-interpreter-exec console \"set breakpoint pending off\""
+
+mi_run_to_main
+
+# Run to a location in the file.
+set bp_location [gdb_get_line_number "set breakpoint here"]
+
+mi_gdb_test "-break-insert ${srcfile}:${bp_location}" \
+    {\^done,bkpt=.number="2",type="breakpoint".*\}} "set breakpoint"
+
+mi_execute_to "exec-continue" "breakpoint-hit" "myfunction" ".*" ".*" "24" \
+    { "" "disp=\"keep\"" } "breakpoint hit"
+
+# Set a breakpoint in a C++ source file whose name contains a
+# Windows-style logical drive.
+mi_gdb_test \
+    "-break-insert -f \"c:/uu.cpp:13\"" \
+    ".*No source file named c:/uu.cpp.*"
