diff -rup a/testsuite/Makefile.am b/testsuite/Makefile.am
--- a/testsuite/Makefile.am	2012-12-16 20:53:45.000000000 -0500
+++ b/testsuite/Makefile.am	2019-06-28 16:59:19.935602953 -0400
@@ -39,6 +39,7 @@ env.exp: Makefile
 	rm -f env.exp
 	echo set libelf_LD_LIBRARY_PATH '"$(libelf_LD_LIBRARY_PATH)"' >> $@
 	echo set libunwind_LD_LIBRARY_PATH '"$(libunwind_LD_LIBRARY_PATH)"' >> $@
+	echo set PREFIX '"$(prefix)"' >> $@
 
 CLEANFILES = *.o *.so *.log *.sum *.ltrace site.bak setval.tmp site.exp env.exp
 
diff -rup a/testsuite/Makefile.in b/testsuite/Makefile.in
--- a/testsuite/Makefile.in	2013-11-04 20:22:47.000000000 -0500
+++ b/testsuite/Makefile.in	2019-06-28 16:59:12.075602806 -0400
@@ -648,6 +648,7 @@ env.exp: Makefile
 	rm -f env.exp
 	echo set libelf_LD_LIBRARY_PATH '"$(libelf_LD_LIBRARY_PATH)"' >> $@
 	echo set libunwind_LD_LIBRARY_PATH '"$(libunwind_LD_LIBRARY_PATH)"' >> $@
+	echo set PREFIX '"$(prefix)"' >> $@
 
 # Tell versions [3.59,3.63) of GNU make to not export all variables.
 # Otherwise a system limit (for SysV at least) may be exceeded.
diff -rup a/testsuite/ltrace.main/system_call_params.exp b/testsuite/ltrace.main/system_call_params.exp
--- a/testsuite/ltrace.main/system_call_params.exp	2019-06-28 16:44:07.542584754 -0400
+++ b/testsuite/ltrace.main/system_call_params.exp	2019-06-28 17:00:35.811604355 -0400
@@ -1,5 +1,5 @@
 # This file is part of ltrace.
-# Copyright (C) 2013, 2014 Petr Machata, Red Hat Inc.
+# Copyright (C) 2013, 2014, 2015 Petr Machata, Red Hat Inc.
 #
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU General Public License as
@@ -60,8 +60,35 @@ set conf [ltraceNamedSource "$dir/syscal
 # somelib.conf is passed, and syscalls.conf is not available, or
 # doesn't list readdir, that would be taken from somelib.conf with a
 # wrong prototype.
+#
+# This test relies on the fact that there is no global config file
+# that would provide legitimate system call prototypes.  But that
+# doesn't have to be true, maybe ltrace is already installed on the
+# system with the right prefix.  So first compile a wrapper that we
+# use to redirect fopen calls.
+
+set libfopen_so [ltraceCompile libfopen.so -ldl \
+		     [ltraceSource c [string map [list "@PREFIX@" "$PREFIX"] {
+    #define _GNU_SOURCE
+    #include <dlfcn.h>
+    #include <stdio.h>
+    #include <string.h>
+
+    FILE *
+    fopen(const char *path, const char *mode)
+    {
+	#define PATH "@PREFIX@/share"
+	if (strncmp(path, PATH, sizeof(PATH) - 1) == 0)
+	    path = "/dev/null";
 
+	return ((FILE *(*)(const char *, const char *))
+		dlsym(RTLD_NEXT, "fopen")) (path, mode);
+    }
+}]]]
+ 
+setenv LD_PRELOAD $libfopen_so
 ltraceMatch1 [ltraceRun -L -S -F $conf -- $bin] {^open@SYS\("/some/path", 0\)} == 0
+unsetenv LD_PRELOAD
 
 # On the other hand, if -F somedir/ is given, we want to accept
 # syscalls.conf found there.