diff --git a/src/test/isolation/Makefile b/src/test/isolation/Makefile
index c027c29ab7638aca626c1a1d19d820a0f3e16e78..6513b5f24ed562cec54fc555e283f5362b6dbffe 100644
--- a/src/test/isolation/Makefile
+++ b/src/test/isolation/Makefile
@@ -72,5 +72,10 @@ maintainer-clean: distclean
 installcheck: all
 	./pg_isolation_regress --inputdir=$(srcdir) --schedule=$(srcdir)/isolation_schedule
 
-check: all
-	./pg_isolation_regress --temp-install=./tmp_check --inputdir=$(srcdir) --top-builddir=$(top_builddir) --schedule=$(srcdir)/isolation_schedule
+# We can't support "make check" because isolationtester requires libpq, and
+# in fact (on typical platforms using shared libraries) requires libpq to
+# already be installed.  You could run "make install" and then run a check
+# using a temp installation, but there seems little point in that.
+check:
+	@echo "'make check' is not supported."
+	@echo "Install PostgreSQL, then 'make installcheck' instead."