diff --git a/tests/data/test1034 b/tests/data/test1034
index cf4d1b2408..eda13bb23e 100644
--- a/tests/data/test1034
+++ b/tests/data/test1034
@@ -28,6 +28,9 @@ http
 proxy
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 HTTP over proxy with malformatted IDN host name
 </name>
diff --git a/tests/data/test1035 b/tests/data/test1035
index 622bb91dde..c8eb282aff 100644
--- a/tests/data/test1035
+++ b/tests/data/test1035
@@ -26,6 +26,9 @@ http
 proxy
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 HTTP over proxy with too long IDN host name
 </name>
diff --git a/tests/data/test955 b/tests/data/test955
index 7585a8abb5..633c2e369d 100644
--- a/tests/data/test955
+++ b/tests/data/test955
@@ -23,6 +23,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP without SMTPUTF8 support - UTF-8 based sender (local part only)
 </name>
diff --git a/tests/data/test956 b/tests/data/test956
index 2211291ea7..9472e96e15 100644
--- a/tests/data/test956
+++ b/tests/data/test956
@@ -20,6 +20,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP without SMTPUTF8 support - UTF-8 based recipient (local part only)
 </name>
diff --git a/tests/data/test957 b/tests/data/test957
index bcb61983a4..671d73bbf2 100644
--- a/tests/data/test957
+++ b/tests/data/test957
@@ -21,6 +21,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP VRFY without SMTPUTF8 support - UTF-8 recipient (local part only)
 </name>
diff --git a/tests/data/test958 b/tests/data/test958
index 6cb04dcd2e..203254bfc2 100644
--- a/tests/data/test958
+++ b/tests/data/test958
@@ -21,6 +21,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP external VRFY without SMTPUTF8 - UTF-8 recipient (local part only)
 </name>
diff --git a/tests/data/test959 b/tests/data/test959
index e04da87d3e..5693e34944 100644
--- a/tests/data/test959
+++ b/tests/data/test959
@@ -24,6 +24,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP without SMTPUTF8 support - UTF-8 based sender (host part only)
 </name>
diff --git a/tests/data/test960 b/tests/data/test960
index e8ba21f982..ced2ba0b54 100644
--- a/tests/data/test960
+++ b/tests/data/test960
@@ -21,6 +21,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP without SMTPUTF8 support - UTF-8 based recipient (host part only)
 </name>
diff --git a/tests/data/test961 b/tests/data/test961
index 18ff9dc044..c52d5df344 100644
--- a/tests/data/test961
+++ b/tests/data/test961
@@ -22,6 +22,9 @@ smtp
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP external VRFY without SMTPUTF8 - UTF-8 recipient (host part only)
 </name>
diff --git a/tests/data/test968 b/tests/data/test968
index 158c6a958d..4df600483b 100644
--- a/tests/data/test968
+++ b/tests/data/test968
@@ -26,6 +26,9 @@ IDN
 !win32
 codeset-utf8
 </features>
+<setenv>
+LC_ALL=C.UTF-8
+</setenv>
 <name>
 SMTP VRFY with SMTPUTF8 support
 </name>