diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cf9dbc503a..d8d956f35e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2017-11-07  Tom Tromey  <tom@tromey.com>
+
+	* source.c (directory_switch, mod_path, add_path): Constify.
+	* defs.h (add_path, mod_path, directory_switch): Constify.
+	* mi/mi-cmd-env.c (env_mod_path): Constify.
+
 2017-11-07  Tom Tromey  <tom@tromey.com>
 
 	* infcmd.c (strip_bg_char): Return gdb::unique_xmalloc_ptr.
diff --git a/gdb/defs.h b/gdb/defs.h
index cf59602857..675c239af2 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -350,11 +350,11 @@ extern int openp (const char *, int, const char *, int, char **);
 
 extern int source_full_path_of (const char *, char **);
 
-extern void mod_path (char *, char **);
+extern void mod_path (const char *, char **);
 
-extern void add_path (char *, char **, int);
+extern void add_path (const char *, char **, int);
 
-extern void directory_switch (char *, int);
+extern void directory_switch (const char *, int);
 
 extern char *source_path;
 
diff --git a/gdb/mi/mi-cmd-env.c b/gdb/mi/mi-cmd-env.c
index 0d08bb89a9..436462ac5f 100644
--- a/gdb/mi/mi-cmd-env.c
+++ b/gdb/mi/mi-cmd-env.c
@@ -32,8 +32,6 @@
 #include "top.h"
 #include <sys/stat.h>
 
-static void env_mod_path (char *dirname, char **which_path);
-
 static const char path_var_name[] = "PATH";
 static char *orig_path = NULL;
 
@@ -94,7 +92,7 @@ mi_cmd_env_cd (const char *command, char **argv, int argc)
 }
 
 static void
-env_mod_path (char *dirname, char **which_path)
+env_mod_path (const char *dirname, char **which_path)
 {
   if (dirname == 0 || dirname[0] == '\0')
     return;
diff --git a/gdb/source.c b/gdb/source.c
index aa672fde45..4ae2ba251b 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -444,7 +444,7 @@ directory_command (char *dirname, int from_tty)
    This will not be quoted so we must not treat spaces as separators.  */
 
 void
-directory_switch (char *dirname, int from_tty)
+directory_switch (const char *dirname, int from_tty)
 {
   add_path (dirname, &source_path, 0);
 }
@@ -452,7 +452,7 @@ directory_switch (char *dirname, int from_tty)
 /* Add zero or more directories to the front of an arbitrary path.  */
 
 void
-mod_path (char *dirname, char **which_path)
+mod_path (const char *dirname, char **which_path)
 {
   add_path (dirname, which_path, 1);
 }
@@ -464,7 +464,7 @@ mod_path (char *dirname, char **which_path)
    as space or tab.  */
 
 void
-add_path (char *dirname, char **which_path, int parse_separators)
+add_path (const char *dirname, char **which_path, int parse_separators)
 {
   char *old = *which_path;
   int prefix = 0;