diff --git a/client/main.h b/client/main.h
index 7db88019d4..7f73ac16ac 100644
--- a/client/main.h
+++ b/client/main.h
@@ -16,9 +16,9 @@
 // along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
 
 #ifdef _WIN32
-extern void log_message_startup(char* msg);
-extern void log_message_error(char* msg);
-extern void log_message_error(char* msg, int error_code);
+extern void log_message_startup(const char* msg);
+extern void log_message_error(const char* msg);
+extern void log_message_error(const char* msg, int error_code);
 extern int boinc_main_loop();
 #endif