diff --git a/client/client_msgs.cpp b/client/client_msgs.cpp
index 356fdddcdb..8c158a90d0 100644
--- a/client/client_msgs.cpp
+++ b/client/client_msgs.cpp
@@ -125,6 +125,11 @@ void show_message(
     // print message to the console
     printf("%s", evt_message);
 
+#ifdef _MSC_VER
+    // MSVCRT doesn't support line buffered streams
+    fflush(stdout);
+#endif
+
     // print message to the debugger view port
     diagnostics_trace_to_debugger(evt_message);  
 }
diff --git a/client/main.cpp b/client/main.cpp
index e4fd1e87e2..0c76d6e8fc 100644
--- a/client/main.cpp
+++ b/client/main.cpp
@@ -83,6 +83,10 @@ void log_message_startup(const char* msg) {
     );
     if (!gstate.executing_as_daemon) {
         fprintf(stdout, "%s", evt_msg);
+#ifdef _MSC_VER
+        // MSVCRT doesn't support line buffered streams
+        fflush(stdout);
+#endif
     } else {
 #ifdef _WIN32
         LogEventInfoMessage(evt_msg);
@@ -373,8 +377,6 @@ int boinc_main_loop() {
         if (!gstate.poll_slow_events()) {
             gstate.do_io_or_sleep(POLL_INTERVAL);
         }
-        fflush(stderr);
-        fflush(stdout);
 
         if (gstate.time_to_exit()) {
             msg_printf(NULL, MSG_INFO, "Time to exit");
diff --git a/lib/diagnostics.cpp b/lib/diagnostics.cpp
index bdd1707497..ec3704abce 100644
--- a/lib/diagnostics.cpp
+++ b/lib/diagnostics.cpp
@@ -352,6 +352,7 @@ int diagnostics_init(
         if (!stdout_file) {
             return ERR_FOPEN;
         }
+        setvbuf(stdout_file, NULL, _IOLBF, BUFSIZ);
     }
 
     if (flags & BOINC_DIAG_REDIRECTSTDOUTOVERWRITE) {
@@ -359,6 +360,7 @@ int diagnostics_init(
         if (!stdout_file) {
             return ERR_FOPEN;
         }
+        setvbuf(stdout_file, NULL, _IOLBF, BUFSIZ);
     }