diff --git a/src/bin/e_start_main.c b/src/bin/e_start_main.c
index c5991bd34..e2011501f 100644
--- a/src/bin/e_start_main.c
+++ b/src/bin/e_start_main.c
@@ -27,9 +27,10 @@ env_set(const char *var, const char *val)
 	setenv(var, val, 1);
 #else
 	char *buf;
+        size_t size = strlen(var) + 1 + strlen(val) + 1;
 
-	buf = alloca(strlen(var) + 1 + strlen(val) + 1);
-	snprintf(buf, sizeof(buf), "%s=%s", var, val);
+	buf = alloca(size;
+	snprintf(buf, size, "%s=%s", var, val);
 	if (getenv(var)) putenv(buf);
 	else putenv(strdup(buf));
 #endif