diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index cdd71a9..578af2e 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -24,6 +24,7 @@
 #include "catalog/index.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_type.h"
+#include "common/link-canary.h"
 #include "libpq/pqsignal.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -503,6 +504,13 @@ BootstrapModeMain(void)
 	Assert(IsBootstrapProcessingMode());
 
 	/*
+	 * To ensure that src/common/link-canary.c is linked into the backend, we
+	 * must call it from somewhere.  Here is as good as anywhere.
+	 */
+	if (pg_link_canary_is_frontend())
+		elog(ERROR, "backend is incorrectly linked to frontend functions");
+
+	/*
 	 * Do backend-like initialization for bootstrap mode
 	 */
 	InitProcess();
diff --git a/src/common/Makefile b/src/common/Makefile
index 1fc2c66..6871747 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -41,7 +41,8 @@ override CPPFLAGS := -DFRONTEND $(CPPFLAGS)
 LIBS += $(PTHREAD_LIBS)
 
 OBJS_COMMON = base64.o config_info.o controldata_utils.o exec.o file_perm.o \
-	ip.o keywords.o md5.o pg_lzcompress.o pgfnames.o psprintf.o relpath.o \
+	ip.o keywords.o link-canary.o md5.o pg_lzcompress.o \
+	pgfnames.o psprintf.o relpath.o \
 	rmtree.o saslprep.o scram-common.o string.o unicode_norm.o \
 	username.o wait_error.o
 
diff --git a/src/common/link-canary.c b/src/common/link-canary.c
new file mode 100644
index 0000000..5b4e562
--- /dev/null
+++ b/src/common/link-canary.c
@@ -0,0 +1,36 @@
+/*-------------------------------------------------------------------------
+ * link-canary.c
+ *	  Detect whether src/common functions came from frontend or backend.
+ *
+ * Copyright (c) 2018, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/common/link-canary.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "c.h"
+
+#include "common/link-canary.h"
+
+/*
+ * This function just reports whether this file was compiled for frontend
+ * or backend environment.  We need this because in some systems, mainly
+ * ELF-based platforms, it is possible for a shlib (such as libpq) loaded
+ * into the backend to call a backend function named XYZ in preference to
+ * the shlib's own function XYZ.  That's bad if the two functions don't
+ * act identically.  This exact situation comes up for many functions in
+ * src/common and src/port, where the same function names exist in both
+ * libpq and the backend but they don't act quite identically.  To verify
+ * that appropriate measures have been taken to prevent incorrect symbol
+ * resolution, libpq should test that this function returns true.
+ */
+bool
+pg_link_canary_is_frontend(void)
+{
+#ifdef FRONTEND
+	return true;
+#else
+	return false;
+#endif
+}
diff --git a/src/include/common/link-canary.h b/src/include/common/link-canary.h
new file mode 100644
index 0000000..917faae
--- /dev/null
+++ b/src/include/common/link-canary.h
@@ -0,0 +1,17 @@
+/*-------------------------------------------------------------------------
+ *
+ * link-canary.h
+ *	  Detect whether src/common functions came from frontend or backend.
+ *
+ * Copyright (c) 2018, PostgreSQL Global Development Group
+ *
+ * src/include/common/link-canary.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef LINK_CANARY_H
+#define LINK_CANARY_H
+
+extern bool pg_link_canary_is_frontend(void);
+
+#endif							/* LINK_CANARY_H */
diff --git a/src/interfaces/libpq/.gitignore b/src/interfaces/libpq/.gitignore
index 5c232ae..ce1576e 100644
--- a/src/interfaces/libpq/.gitignore
+++ b/src/interfaces/libpq/.gitignore
@@ -25,6 +25,7 @@
 /ip.c
 /md5.c
 /base64.c
+/link-canary.c
 /scram-common.c
 /sha2.c
 /sha2_openssl.c
diff --git a/src/interfaces/libpq/Makefile b/src/interfaces/libpq/Makefile
index abe0a50..ec0122a 100644
--- a/src/interfaces/libpq/Makefile
+++ b/src/interfaces/libpq/Makefile
@@ -49,7 +49,7 @@ endif
 # src/backend/utils/mb
 OBJS += encnames.o wchar.o
 # src/common
-OBJS += base64.o ip.o md5.o scram-common.o saslprep.o unicode_norm.o
+OBJS += base64.o ip.o link-canary.o md5.o scram-common.o saslprep.o unicode_norm.o
 
 ifeq ($(with_openssl),yes)
 OBJS += fe-secure-openssl.o fe-secure-common.o sha2_openssl.o
@@ -106,7 +106,7 @@ backend_src = $(top_srcdir)/src/backend
 chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c: % : $(top_srcdir)/src/port/%
 	rm -f $@ && $(LN_S) $< .
 
-ip.c md5.c base64.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c: % : $(top_srcdir)/src/common/%
+ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c: % : $(top_srcdir)/src/common/%
 	rm -f $@ && $(LN_S) $< .
 
 encnames.c wchar.c: % : $(backend_src)/utils/mb/%
@@ -156,7 +156,7 @@ clean distclean: clean-lib
 	rm -f pg_config_paths.h
 # Remove files we (may have) symlinked in from src/port and other places
 	rm -f chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c
-	rm -f ip.c md5.c base64.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c
+	rm -f ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c
 	rm -f encnames.c wchar.c
 
 maintainer-clean: distclean maintainer-clean-lib
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index db5aacd..42cdb97 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -71,6 +71,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
 #endif
 
 #include "common/ip.h"
+#include "common/link-canary.h"
 #include "common/scram-common.h"
 #include "mb/pg_wchar.h"
 #include "port/pg_bswap.h"
@@ -1748,6 +1749,19 @@ connectDBStart(PGconn *conn)
 	if (!conn->options_valid)
 		goto connect_errReturn;
 
+	/*
+	 * Check for bad linking to backend-internal versions of src/common
+	 * functions (see comments in link-canary.c for the reason we need this).
+	 * Nobody but developers should see this message, so we don't bother
+	 * translating it.
+	 */
+	if (!pg_link_canary_is_frontend())
+	{
+		printfPQExpBuffer(&conn->errorMessage,
+						  "libpq is incorrectly linked to backend functions\n");
+		goto connect_errReturn;
+	}
+
 	/* Ensure our buffers are empty */
 	conn->inStart = conn->inCursor = conn->inEnd = 0;
 	conn->outCount = 0;
diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index 14d2a3c..9ce03ce 100644
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -116,7 +116,8 @@ sub mkvcbuild
 
 	our @pgcommonallfiles = qw(
 	  base64.c config_info.c controldata_utils.c exec.c file_perm.c ip.c
-	  keywords.c md5.c pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c
+	  keywords.c link-canary.c md5.c
+	  pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c
 	  saslprep.c scram-common.c string.c unicode_norm.c username.c
 	  wait_error.c);