diff --git a/src/plugins/mail-filter/istream-ext-filter.c b/src/plugins/mail-filter/istream-ext-filter.c
index 5bd90774f8..31746b1e55 100644
--- a/src/plugins/mail-filter/istream-ext-filter.c
+++ b/src/plugins/mail-filter/istream-ext-filter.c
@@ -2,6 +2,7 @@
 
 #include "lib.h"
 #include "str.h"
+#include "strescape.h"
 #include "net.h"
 #include "eacces-error.h"
 #include "fd-set-nonblock.h"
@@ -175,8 +176,8 @@ static int filter_connect(struct mail_filter_istream *mstream,
 	str = t_str_new(256);
 	str_append(str, "VERSION\tscript\t4\t0\nnoreply\n");
 	for (; *argv != NULL; argv++) {
-		str_append(str, *argv);
-		str_append_c(str, '\n');
+		str_append_tabescaped(str, *argv);
+		str_append_c(str, '\t');
 	}
 	str_append_c(str, '\n');
 
diff --git a/src/plugins/mail-filter/ostream-ext-filter.c b/src/plugins/mail-filter/ostream-ext-filter.c
index 4ebfce08af..3e8f6020f7 100644
--- a/src/plugins/mail-filter/ostream-ext-filter.c
+++ b/src/plugins/mail-filter/ostream-ext-filter.c
@@ -2,6 +2,7 @@
 
 #include "lib.h"
 #include "str.h"
+#include "strescape.h"
 #include "net.h"
 #include "eacces-error.h"
 #include "istream.h"
@@ -148,8 +149,8 @@ static int filter_connect(struct mail_filter_ostream *mstream,
 	str = t_str_new(256);
 	str_append(str, "VERSION\tscript\t4\t0\nnoreply\n");
 	for (; *argv != NULL; argv++) {
-		str_append(str, *argv);
-		str_append_c(str, '\n');
+		str_append_tabescaped(str, *argv);
+		str_append_c(str, '\t');
 	}
 	str_append_c(str, '\n');