diff --git a/kitty/child.py b/kitty/child.py
index 7f4e998ad..a2edabb93 100644
--- a/kitty/child.py
+++ b/kitty/child.py
@@ -252,7 +252,7 @@ class Child:
         env['KITTY_PID'] = getpid()
         if not self.is_prewarmed:
             env['KITTY_PREWARM_SOCKET'] = fast_data_types.get_boss().prewarm.socket_env_var()
-            env['KITTY_PREWARM_SOCKET_REAL_TTY'] = '0' * 32
+            env['KITTY_PREWARM_SOCKET_REAL_TTY'] = ' ' * 32
         if self.cwd:
             # needed in case cwd is a symlink, in which case shells
             # can use it to display the current directory name rather
diff --git a/kitty_tests/prewarm.py b/kitty_tests/prewarm.py
index 45c0442d1..108562aa4 100644
--- a/kitty_tests/prewarm.py
+++ b/kitty_tests/prewarm.py
@@ -68,7 +68,7 @@ def socket_child_main(exit_code=0, initial_print=''):
         env.update({
             'TEST_ENV_PASS': 'xyz',
             'KITTY_PREWARM_SOCKET': p.socket_env_var(),
-            'KITTY_PREWARM_SOCKET_REAL_TTY': '0' * 32,
+            'KITTY_PREWARM_SOCKET_REAL_TTY': ' ' * 32,
             'TERM': 'xterm-kitty',
             'TERMINFO': terminfo_dir
         })
diff --git a/prewarm-launcher.c b/prewarm-launcher.c
index bc822e228..f6304894b 100644
--- a/prewarm-launcher.c
+++ b/prewarm-launcher.c
@@ -44,6 +44,9 @@
 #define MAX(x, y) __extension__ ({ \
     __typeof__ (x) a = (x); __typeof__ (y) b = (y); \
         a > b ? a : b;})
+#define MIN(x, y) __extension__ ({ \
+    __typeof__ (x) a = (x); __typeof__ (y) b = (y); \
+        a < b ? a : b;})
 // }}}
 
 #define IO_BUZ_SZ 8192
@@ -700,7 +703,8 @@ use_prewarmed_process(int argc, char *argv[], char *envp[]) {
 
     while (*envp) {
         if (strncmp(*envp, "KITTY_PREWARM_SOCKET_REAL_TTY=", 2) == 0) {
-            sprintf(*envp,  "KITTY_PREWARM_SOCKET_REAL_TTY=%s", child_tty_name);
+            char *p = *envp + sizeof("KITTY_PREWARM_SOCKET_REAL_TTY=") - 1;
+            snprintf(p, strlen(p) + 1, "%s", child_tty_name);
         }
         envp++;
     }