diff --git a/.gitignore b/.gitignore
index 9d1363a1eb..f7b7977910 100644
--- a/.gitignore
+++ b/.gitignore
@@ -148,6 +148,7 @@
 /git-serve
 /git-sh-i18n
 /git-sh-i18n--envsubst
+/git-sh-i18n--helper
 /git-sh-setup
 /git-sh-i18n
 /git-shell
diff --git a/.travis.yml b/.travis.yml
index 4d4e26c9df..4523a2e5ec 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,7 +26,7 @@ addons:
 
 matrix:
   include:
-    - env: jobname=GETTEXT_POISON
+    - env: jobname=GIT_TEST_GETTEXT_POISON
       os: linux
       compiler:
       addons:
diff --git a/Makefile b/Makefile
index d18ab0fe78..684dec4d39 100644
--- a/Makefile
+++ b/Makefile
@@ -362,11 +362,6 @@ all::
 # Define HAVE_DEV_TTY if your system can open /dev/tty to interact with the
 # user.
 #
-# Define GETTEXT_POISON if you are debugging the choice of strings marked
-# for translation.  In a GETTEXT_POISON build, you can turn all strings marked
-# for translation into gibberish by setting the GIT_GETTEXT_POISON variable
-# (to any value) in your environment.
-#
 # Define JSMIN to point to JavaScript minifier that functions as
 # a filter to have gitweb.js minified.
 #
@@ -714,6 +709,7 @@ TEST_BUILTINS_OBJS += test-dump-split-index.o
 TEST_BUILTINS_OBJS += test-dump-untracked-cache.o
 TEST_BUILTINS_OBJS += test-example-decorate.o
 TEST_BUILTINS_OBJS += test-genrandom.o
+TEST_BUILTINS_OBJS += test-gettext-poison.o
 TEST_BUILTINS_OBJS += test-hashmap.o
 TEST_BUILTINS_OBJS += test-index-version.o
 TEST_BUILTINS_OBJS += test-json-writer.o
@@ -1099,6 +1095,7 @@ BUILTIN_OBJS += builtin/revert.o
 BUILTIN_OBJS += builtin/rm.o
 BUILTIN_OBJS += builtin/send-pack.o
 BUILTIN_OBJS += builtin/serve.o
+BUILTIN_OBJS += builtin/sh-i18n--helper.o
 BUILTIN_OBJS += builtin/shortlog.o
 BUILTIN_OBJS += builtin/show-branch.o
 BUILTIN_OBJS += builtin/show-index.o
@@ -1439,9 +1436,6 @@ endif
 ifdef NO_SYMLINK_HEAD
 	BASIC_CFLAGS += -DNO_SYMLINK_HEAD
 endif
-ifdef GETTEXT_POISON
-	BASIC_CFLAGS += -DGETTEXT_POISON
-endif
 ifdef NO_GETTEXT
 	BASIC_CFLAGS += -DNO_GETTEXT
 	USE_GETTEXT_SCHEME ?= fallthrough
@@ -2591,7 +2585,6 @@ ifdef GIT_TEST_CMP_USE_COPIED_CONTEXT
 	@echo GIT_TEST_CMP_USE_COPIED_CONTEXT=YesPlease >>$@+
 endif
 	@echo NO_GETTEXT=\''$(subst ','\'',$(subst ','\'',$(NO_GETTEXT)))'\' >>$@+
-	@echo GETTEXT_POISON=\''$(subst ','\'',$(subst ','\'',$(GETTEXT_POISON)))'\' >>$@+
 ifdef GIT_PERF_REPEAT_COUNT
 	@echo GIT_PERF_REPEAT_COUNT=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPEAT_COUNT)))'\' >>$@+
 endif
diff --git a/builtin.h b/builtin.h
index 962f0489ab..a40c56e7a2 100644
--- a/builtin.h
+++ b/builtin.h
@@ -219,6 +219,7 @@ extern int cmd_revert(int argc, const char **argv, const char *prefix);
 extern int cmd_rm(int argc, const char **argv, const char *prefix);
 extern int cmd_send_pack(int argc, const char **argv, const char *prefix);
 extern int cmd_serve(int argc, const char **argv, const char *prefix);
+extern int cmd_sh_i18n__helper(int argc, const char **argv, const char *prefix);
 extern int cmd_shortlog(int argc, const char **argv, const char *prefix);
 extern int cmd_show(int argc, const char **argv, const char *prefix);
 extern int cmd_show_branch(int argc, const char **argv, const char *prefix);
diff --git a/builtin/sh-i18n--helper.c b/builtin/sh-i18n--helper.c
new file mode 100644
index 0000000000..1fba8b902b
--- /dev/null
+++ b/builtin/sh-i18n--helper.c
@@ -0,0 +1,27 @@
+#include "builtin.h"
+#include "cache.h"
+#include "config.h"
+#include "parse-options.h"
+
+static const char * const builtin_sh_i18n_helper_usage[] = {
+	N_("git sh-i18n--helper [<options>]"),
+	NULL
+};
+
+int cmd_sh_i18n__helper(int argc, const char **argv, const char *prefix)
+{
+	int poison = -1;
+	struct option options[] = {
+		OPT_BOOL(0, "git-test-gettext-poison", &poison,
+			 N_("is GIT_TEST_GETTEXT_POISON in effect?")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     builtin_sh_i18n_helper_usage, PARSE_OPT_KEEP_ARGV0);
+
+	if (poison != -1)
+		return !git_env_bool("GIT_TEST_GETTEXT_POISON", 0);
+
+	usage_with_options(builtin_sh_i18n_helper_usage, options);
+}
diff --git a/ci/lib-travisci.sh b/ci/lib-travisci.sh
index 06970f7213..6a89d0d7d8 100755
--- a/ci/lib-travisci.sh
+++ b/ci/lib-travisci.sh
@@ -123,7 +123,7 @@ osx-clang|osx-gcc)
 	# Travis CI OS X
 	export GIT_SKIP_TESTS="t9810 t9816"
 	;;
-GETTEXT_POISON)
-	export GETTEXT_POISON=YesPlease
+GIT_TEST_GETTEXT_POISON)
+	export GIT_TEST_GETTEXT_POISON=true
 	;;
 esac
diff --git a/gettext.c b/gettext.c
index 7272771c8e..722a2f726c 100644
--- a/gettext.c
+++ b/gettext.c
@@ -7,6 +7,7 @@
 #include "gettext.h"
 #include "strbuf.h"
 #include "utf8.h"
+#include "config.h"
 
 #ifndef NO_GETTEXT
 #	include <locale.h>
@@ -46,15 +47,13 @@ const char *get_preferred_languages(void)
 	return NULL;
 }
 
-#ifdef GETTEXT_POISON
 int use_gettext_poison(void)
 {
 	static int poison_requested = -1;
 	if (poison_requested == -1)
-		poison_requested = getenv("GIT_GETTEXT_POISON") ? 1 : 0;
+		poison_requested = git_env_bool("GIT_TEST_GETTEXT_POISON", 0);
 	return poison_requested;
 }
-#endif
 
 #ifndef NO_GETTEXT
 static int test_vsnprintf(const char *fmt, ...)
diff --git a/gettext.h b/gettext.h
index 7eee64a34f..4c492d9f57 100644
--- a/gettext.h
+++ b/gettext.h
@@ -41,11 +41,7 @@ static inline int gettext_width(const char *s)
 }
 #endif
 
-#ifdef GETTEXT_POISON
 extern int use_gettext_poison(void);
-#else
-#define use_gettext_poison() 0
-#endif
 
 static inline FORMAT_PRESERVING(1) const char *_(const char *msgid)
 {
diff --git a/git-sh-i18n.sh b/git-sh-i18n.sh
index 9d065fb4bf..c0713b1ee9 100644
--- a/git-sh-i18n.sh
+++ b/git-sh-i18n.sh
@@ -17,7 +17,8 @@ export TEXTDOMAINDIR
 
 # First decide what scheme to use...
 GIT_INTERNAL_GETTEXT_SH_SCHEME=fallthrough
-if test -n "$GIT_GETTEXT_POISON"
+if test -n "$GIT_TEST_GETTEXT_POISON" &&
+	    git sh-i18n--helper --git-test-gettext-poison
 then
 	GIT_INTERNAL_GETTEXT_SH_SCHEME=poison
 elif test -n "@@USE_GETTEXT_SCHEME@@"
diff --git a/git.c b/git.c
index 5920f8019b..125c523720 100644
--- a/git.c
+++ b/git.c
@@ -539,6 +539,7 @@ static struct cmd_struct commands[] = {
 	{ "rm", cmd_rm, RUN_SETUP },
 	{ "send-pack", cmd_send_pack, RUN_SETUP },
 	{ "serve", cmd_serve, RUN_SETUP },
+	{ "sh-i18n--helper", cmd_sh_i18n__helper, 0 },
 	{ "shortlog", cmd_shortlog, RUN_SETUP_GENTLY | USE_PAGER },
 	{ "show", cmd_show, RUN_SETUP },
 	{ "show-branch", cmd_show_branch, RUN_SETUP },
diff --git a/po/README b/po/README
index fef4c0f0b5..dba46c4a40 100644
--- a/po/README
+++ b/po/README
@@ -289,16 +289,11 @@ something in the test suite might still depend on the US English
 version of the strings, e.g. to grep some error message or other
 output.
 
-To smoke out issues like these Git can be compiled with gettext poison
-support, at the top-level:
+To smoke out issues like these Git tested with a translation mode that
+emits gibberish on every call to gettext. To use it run the test suite
+with it, e.g.:
 
-    make GETTEXT_POISON=YesPlease
-
-That'll give you a git which emits gibberish on every call to
-gettext. It's obviously not meant to be installed, but you should run
-the test suite with it:
-
-    cd t && prove -j 9 ./t[0-9]*.sh
+    cd t && GIT_TEST_GETTEXT_POISON=true prove -j 9 ./t[0-9]*.sh
 
 If tests break with it you should inspect them manually and see if
 what you're translating is sane, i.e. that you're not translating
diff --git a/t/README b/t/README
index 8847489640..53c3dee7a9 100644
--- a/t/README
+++ b/t/README
@@ -301,6 +301,12 @@ that cannot be easily covered by a few specific test cases. These
 could be enabled by running the test suite with correct GIT_TEST_
 environment set.
 
+GIT_TEST_GETTEXT_POISON=<boolean> turns all strings marked for
+translation into gibberish. Used for spotting those tests that need to
+be marked with a C_LOCALE_OUTPUT prerequisite when adding more strings
+for translation. See "Testing marked strings" in po/README for
+details.
+
 GIT_TEST_SPLIT_INDEX=<boolean> forces split-index mode on the whole
 test suite. Accept any boolean values that are accepted by git-config.
 
diff --git a/t/helper/test-gettext-poison.c b/t/helper/test-gettext-poison.c
new file mode 100644
index 0000000000..476be95da5
--- /dev/null
+++ b/t/helper/test-gettext-poison.c
@@ -0,0 +1,9 @@
+#include "test-tool.h"
+#include "git-compat-util.h"
+#include "thread-utils.h"
+#include "gettext.h"
+
+int cmd__gettext_poison(int argc, const char **argv)
+{
+	return use_gettext_poison() ? 0 : 1;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 6b5836dc1b..3e75672a37 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -19,6 +19,7 @@ static struct test_cmd cmds[] = {
 	{ "dump-untracked-cache", cmd__dump_untracked_cache },
 	{ "example-decorate", cmd__example_decorate },
 	{ "genrandom", cmd__genrandom },
+	{ "gettext-poison", cmd__gettext_poison },
 	{ "hashmap", cmd__hashmap },
 	{ "index-version", cmd__index_version },
 	{ "json-writer", cmd__json_writer },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index e4890566da..04f033b7fc 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -15,6 +15,7 @@ int cmd__dump_split_index(int argc, const char **argv);
 int cmd__dump_untracked_cache(int argc, const char **argv);
 int cmd__example_decorate(int argc, const char **argv);
 int cmd__genrandom(int argc, const char **argv);
+int cmd__gettext_poison(int argc, const char **argv);
 int cmd__hashmap(int argc, const char **argv);
 int cmd__index_version(int argc, const char **argv);
 int cmd__json_writer(int argc, const char **argv);
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 4d23373526..b6566003dd 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -274,7 +274,7 @@ test_expect_success 'pretend we have a mix of all possible results' "
 	EOF
 "
 
-test_expect_success 'test --verbose' '
+test_expect_success C_LOCALE_OUTPUT 'test --verbose' '
 	test_must_fail run_sub_test_lib_test \
 		test-verbose "test verbose" --verbose <<-\EOF &&
 	test_expect_success "passing test" true
diff --git a/t/t3406-rebase-message.sh b/t/t3406-rebase-message.sh
index 0392e36d23..2bdcf83808 100755
--- a/t/t3406-rebase-message.sh
+++ b/t/t3406-rebase-message.sh
@@ -77,7 +77,7 @@ test_expect_success 'rebase -n overrides config rebase.stat config' '
 #     "Does not point to a valid commit: invalid-ref"
 #
 # NEEDSWORK: This "grep" is fine in real non-C locales, but
-# GETTEXT_POISON poisons the refname along with the enclosing
+# GIT_TEST_GETTEXT_POISON poisons the refname along with the enclosing
 # error message.
 test_expect_success 'rebase --onto outputs the invalid ref' '
 	test_must_fail git rebase --onto invalid-ref HEAD HEAD 2>err &&
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index 826987ca80..cb2c8cf3f3 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -256,7 +256,10 @@ test_expect_success 'checkout to detach HEAD' '
 	git checkout -f renamer && git clean -f &&
 	git checkout renamer^ 2>messages &&
 	test_i18ngrep "HEAD is now at 7329388" messages &&
-	(test_line_count -gt 1 messages || test -n "$GETTEXT_POISON") &&
+	(
+		test_line_count -gt 1 messages ||
+		test_have_prereq GETTEXT_POISON
+	) &&
 	H=$(git rev-parse --verify HEAD) &&
 	M=$(git show-ref -s --verify refs/heads/master) &&
 	test "z$H" = "z$M" &&
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 78d8c3783b..f46e21cfa0 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -755,16 +755,16 @@ test_cmp_bin() {
 
 # Use this instead of test_cmp to compare files that contain expected and
 # actual output from git commands that can be translated.  When running
-# under GETTEXT_POISON this pretends that the command produced expected
+# under GIT_TEST_GETTEXT_POISON this pretends that the command produced expected
 # results.
 test_i18ncmp () {
-	test -n "$GETTEXT_POISON" || test_cmp "$@"
+	! test_have_prereq C_LOCALE_OUTPUT || test_cmp "$@"
 }
 
 # Use this instead of "grep expected-string actual" to see if the
 # output from a git command that can be translated either contains an
 # expected string, or does not contain an unwanted one.  When running
-# under GETTEXT_POISON this pretends that the command produced expected
+# under GIT_TEST_GETTEXT_POISON this pretends that the command produced expected
 # results.
 test_i18ngrep () {
 	eval "last_arg=\${$#}"
@@ -779,7 +779,7 @@ test_i18ngrep () {
 		error "bug in the test script: too few parameters to test_i18ngrep"
 	fi
 
-	if test -n "$GETTEXT_POISON"
+	if ! test_have_prereq C_LOCALE_OUTPUT
 	then
 		# pretend success
 		return 0
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 897e6fcc94..ec77aa57d4 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1104,15 +1104,8 @@ test -n "$USE_LIBPCRE1" && test_set_prereq LIBPCRE1
 test -n "$USE_LIBPCRE2" && test_set_prereq LIBPCRE2
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT
 
-# Can we rely on git's output in the C locale?
-if test -n "$GETTEXT_POISON"
-then
-	GIT_GETTEXT_POISON=YesPlease
-	export GIT_GETTEXT_POISON
-	test_set_prereq GETTEXT_POISON
-else
-	test_set_prereq C_LOCALE_OUTPUT
-fi
+test-tool gettext-poison && test_set_prereq GETTEXT_POISON
+test-tool gettext-poison || test_set_prereq C_LOCALE_OUTPUT
 
 if test -z "$GIT_TEST_CHECK_CACHE_TREE"
 then
