diff --git a/test/util.cc b/test/util.cc
index d48bdc0e..7b1cdb57 100644
--- a/test/util.cc
+++ b/test/util.cc
@@ -50,12 +50,12 @@ std::string get_system_error(int error_code) {
 #endif
 }
 
-const char *FILE_CONTENT = "Don't panic!";
+const char *const FILE_CONTENT = "Don't panic!";
 
 fmt::BufferedFile open_buffered_file(FILE **fp) {
   fmt::File read_end, write_end;
   fmt::File::pipe(read_end, write_end);
-  write_end.write(FILE_CONTENT, sizeof(FILE_CONTENT) - 1);
+  write_end.write(FILE_CONTENT, std::strlen(FILE_CONTENT));
   write_end.close();
   fmt::BufferedFile f = read_end.fdopen("r");
   if (fp)
diff --git a/test/util.h b/test/util.h
index dc69bef1..4027685c 100644
--- a/test/util.h
+++ b/test/util.h
@@ -52,7 +52,7 @@ void increment(char *s);
 
 std::string get_system_error(int error_code);
 
-extern const char *FILE_CONTENT;
+extern const char *const FILE_CONTENT;
 
 // Opens a buffered file for reading.
 fmt::BufferedFile open_buffered_file(FILE **fp = 0);