diff --git a/src/include/port.h b/src/include/port.h
index 6e21f6e0907..e8b7a35be6e 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -550,7 +550,10 @@ extern int	pg_check_dir(const char *dir);
 /* port/pgmkdirp.c */
 extern int	pg_mkdir_p(char *path, int omode);
 
-/* port/pqsignal.c */
+/* port/pqsignal.c (see also interfaces/libpq/legacy-pqsignal.c) */
+#ifdef FRONTEND
+#define pqsignal pqsignal_fe
+#endif
 typedef void (*pqsigfunc) (int signo);
 extern pqsigfunc pqsignal(int signo, pqsigfunc func);
 
diff --git a/src/interfaces/libpq/legacy-pqsignal.c b/src/interfaces/libpq/legacy-pqsignal.c
index 4703adbf0cc..de5f8963588 100644
--- a/src/interfaces/libpq/legacy-pqsignal.c
+++ b/src/interfaces/libpq/legacy-pqsignal.c
@@ -28,10 +28,16 @@
  * with the semantics it had in 9.2; in particular, this has different
  * behavior for SIGALRM than the version in src/port/pqsignal.c.
  *
- * libpq itself uses this only for SIGPIPE (and even then, only in
- * non-ENABLE_THREAD_SAFETY builds), so the incompatibility isn't
- * troublesome for internal references.
+ * libpq itself does not use this, nor does anything else in our code.
+ *
+ * src/include/port.h will #define pqsignal as pqsignal_fe,
+ * but here we want to export just plain "pqsignal".  We can't rely on
+ * port.h's extern declaration either.  (The point of that #define
+ * is to ensure that no in-tree code accidentally calls this version.)
  */
+#undef pqsignal
+extern pqsigfunc pqsignal(int signo, pqsigfunc func);
+
 pqsigfunc
 pqsignal(int signo, pqsigfunc func)
 {
diff --git a/src/port/pqsignal.c b/src/port/pqsignal.c
index 9bd0068d9a7..215df56bda2 100644
--- a/src/port/pqsignal.c
+++ b/src/port/pqsignal.c
@@ -35,6 +35,10 @@
  * Set up a signal handler, with SA_RESTART, for signal "signo"
  *
  * Returns the previous handler.
+ *
+ * Note: the actual name of this function is either pqsignal_fe when
+ * compiled with -DFRONTEND, or pqsignal when compiled without that.
+ * This is to avoid a name collision with libpq's legacy-pqsignal.c.
  */
 pqsigfunc
 pqsignal(int signo, pqsigfunc func)