diff --git a/.gitignore b/.gitignore
index 3b7680ea1e5baa58430798a9836481975dbb6234..d284b058a33dfa8235d8608a89a500bfef1c1028 100644
--- a/.gitignore
+++ b/.gitignore
@@ -184,6 +184,7 @@
 /test-obj-pool
 /test-parse-options
 /test-path-utils
+/test-regex
 /test-run-command
 /test-sha1
 /test-sigchain
diff --git a/Makefile b/Makefile
index e4f8e0ef08b9f3f4eb5035f20421ee035127fdf2..d2b145b533485d9064c5e2db76949dd5b3a41863 100644
--- a/Makefile
+++ b/Makefile
@@ -476,6 +476,7 @@ TEST_PROGRAMS_NEED_X += test-mktemp
 TEST_PROGRAMS_NEED_X += test-obj-pool
 TEST_PROGRAMS_NEED_X += test-parse-options
 TEST_PROGRAMS_NEED_X += test-path-utils
+TEST_PROGRAMS_NEED_X += test-regex
 TEST_PROGRAMS_NEED_X += test-run-command
 TEST_PROGRAMS_NEED_X += test-sha1
 TEST_PROGRAMS_NEED_X += test-sigchain
diff --git a/t/t0070-fundamental.sh b/t/t0070-fundamental.sh
index 9bee8bfd2e063c40bae2d76930370bd9e8ba8fa5..da2c504e53e37840f71790d6b262106b7b57d697 100755
--- a/t/t0070-fundamental.sh
+++ b/t/t0070-fundamental.sh
@@ -25,4 +25,9 @@ test_expect_success POSIXPERM 'mktemp to unwritable directory prints filename' '
 	grep "cannotwrite/test" err
 '
 
+test_expect_success 'check for a bug in the regex routines' '
+	# if this test fails, re-build git with NO_REGEX=1
+	test-regex
+'
+
 test_done
diff --git a/test-regex.c b/test-regex.c
new file mode 100644
index 0000000000000000000000000000000000000000..b5bfd54139fda811a30a4e56a7098bccba7039ce
--- /dev/null
+++ b/test-regex.c
@@ -0,0 +1,20 @@
+#include <git-compat-util.h>
+
+int main(int argc, char **argv)
+{
+	char *pat = "[^={} \t]+";
+	char *str = "={}\nfred";
+	regex_t r;
+	regmatch_t m[1];
+
+	if (regcomp(&r, pat, REG_EXTENDED | REG_NEWLINE))
+		die("failed regcomp() for pattern '%s'", pat);
+	if (regexec(&r, str, 1, m, 0))
+		die("no match of pattern '%s' to string '%s'", pat, str);
+
+	/* http://sourceware.org/bugzilla/show_bug.cgi?id=3957  */
+	if (m[0].rm_so == 3) /* matches '\n' when it should not */
+		die("regex bug confirmed: re-build git with NO_REGEX=1");
+
+	exit(0);
+}