diff --git a/find/print.h b/find/print.h
index f444295d..79ec7911 100644
--- a/find/print.h
+++ b/find/print.h
@@ -14,6 +14,9 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
+#ifndef PRINT_H
+#define PRINT_H
+
 #include "defs.h"
 
 struct format_val;
@@ -30,3 +33,5 @@ bool
 insert_fprintf (struct format_val *vec,
 		const struct parser_table *entry,
 		char *format);
+
+#endif /* PRINT_H */
diff --git a/lib/fdleak.h b/lib/fdleak.h
index dc6534fb..3c97b6fd 100644
--- a/lib/fdleak.h
+++ b/lib/fdleak.h
@@ -14,9 +14,13 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
+#ifndef FDLEAK_H
+#define FDLEAK_H
 
 void remember_non_cloexec_fds (void);
 void forget_non_cloexec_fds (void);
 void complain_about_leaky_fds (void);
 
 int open_cloexec(const char *path, int flags, ...);
+
+#endif
diff --git a/lib/findutils-version.h b/lib/findutils-version.h
index e1bc2a5d..08b2146d 100644
--- a/lib/findutils-version.h
+++ b/lib/findutils-version.h
@@ -14,7 +14,8 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
-
+#ifndef FINDUTILS_VERSION_H
+#define FINDUTILS_VERSION_H
 /*
  * display_findutils_version displays GNU coding standard compliant
  * version information.
@@ -25,3 +26,5 @@
  *
  */
 void display_findutils_version(const char *official_name);
+
+#endif
diff --git a/lib/regextype.h b/lib/regextype.h
index 093b5a01..49e6c01d 100644
--- a/lib/regextype.h
+++ b/lib/regextype.h
@@ -17,6 +17,8 @@
 */
 /* Written by James Youngman <jay@gnu.org>.
  */
+#ifndef REGEXTPE_H
+#define REGEXTPE_H
 
 /* Translate a regular expression type name into an option mask.
  * This could convert "grep" into RE_SYNTAX_GREP, for example.
@@ -55,3 +57,5 @@ int get_regex_type_synonym(unsigned int ix, unsigned int context);
  * respectively, findutils, general callers, or all callers.
  */
 unsigned int get_regex_type_context(unsigned int ix);
+
+#endif
diff --git a/lib/splitstring.h b/lib/splitstring.h
index 6b3f13f0..5c04e83a 100644
--- a/lib/splitstring.h
+++ b/lib/splitstring.h
@@ -17,6 +17,8 @@
 /*
  * Written by James Youngman.
  */
+#ifndef SPLITSTRING_H
+#define SPLITSTRING_H
 
 /* Split a string into fields.   The string is never modified.
  *
@@ -38,3 +40,5 @@
 
 bool splitstring(const char *s, const char *separators,
 		 bool first, size_t *pos, size_t *len);
+
+#endif