diff --git a/regress/Makefile b/regress/Makefile
index ff58eef40..c354a8187 100644
--- a/regress/Makefile
+++ b/regress/Makefile
@@ -9,7 +9,9 @@ all:
 		printf '%-40s ' "$$test"; \
 		start=$$(date +%s); \
 		ASAN_OPTIONS="abort_on_error=1:detect_leaks=0:$$ASAN_OPTIONS"; \
-		if env -i ASAN_OPTIONS="$$ASAN_OPTIONS" sh "$$test" >/dev/null 2>&1; then \
+		env -i LC_CTYPE=C.UTF-8 ASAN_OPTIONS="$$ASAN_OPTIONS" \
+		    sh "$$test" >/dev/null 2>&1; \
+		if [ $$? -eq 0 ]; then \
 			end=$$(date +%s); \
 			echo "PASS ($$((end - start))s)"; \
 		else \
diff --git a/regress/pane-ops.sh b/regress/pane-ops.sh
index 40e4bb77c..46984bc27 100644
--- a/regress/pane-ops.sh
+++ b/regress/pane-ops.sh
@@ -25,6 +25,9 @@
 
 PATH=/bin:/usr/bin
 TERM=screen
+LANG=C.UTF-8
+LC_ALL=C.UTF-8
+export TERM LANG LC_ALL
 
 [ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
 TMUX="$TEST_TMUX -Ltest -f/dev/null"
diff --git a/regress/session-ops.sh b/regress/session-ops.sh
index 3b4f10073..4938ee22c 100644
--- a/regress/session-ops.sh
+++ b/regress/session-ops.sh
@@ -22,6 +22,9 @@
 
 PATH=/bin:/usr/bin
 TERM=screen
+LANG=C.UTF-8
+LC_ALL=C.UTF-8
+export TERM LANG LC_ALL
 
 [ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
 TMUX="$TEST_TMUX -Ltest -f/dev/null"
diff --git a/regress/window-ops.sh b/regress/window-ops.sh
index 3dba68edd..dde7fc957 100644
--- a/regress/window-ops.sh
+++ b/regress/window-ops.sh
@@ -25,6 +25,9 @@
 
 PATH=/bin:/usr/bin
 TERM=screen
+LANG=C.UTF-8
+LC_ALL=C.UTF-8
+export TERM LANG LC_ALL
 
 [ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
 TMUX="$TEST_TMUX -Ltest -f/dev/null"