diff --git a/cmdline/check.c b/cmdline/check.c
index f1d4ac72..81a720c6 100644
--- a/cmdline/check.c
+++ b/cmdline/check.c
@@ -1809,7 +1809,7 @@ bail:
 		else
 			ftag("summary:exit:error\n");
 	}
-	fflush(stdlog);
+	fflush_log();
 
 	free(failed);
 	free(failed_map);
diff --git a/cmdline/dup.c b/cmdline/dup.c
index 9ee4bfa7..2945c0c9 100644
--- a/cmdline/dup.c
+++ b/cmdline/dup.c
@@ -151,6 +151,6 @@ void state_dup(struct snapraid_state* state)
 	} else {
 		ftag("summary:exit:dup\n");
 	}
-	fflush(stdlog);
+	fflush_log();
 }
 
diff --git a/cmdline/list.c b/cmdline/list.c
index 6b9e2d3e..c9cd07cb 100644
--- a/cmdline/list.c
+++ b/cmdline/list.c
@@ -117,6 +117,6 @@ void state_list(struct snapraid_state* state)
 	ftag("summary:file_size:%" PRIu64 "\n", file_size);
 	ftag("summary:link_count:%u\n", link_count);
 	ftag("summary:exit:ok\n");
-	fflush(stdlog);
+	fflush_log();
 }
 
diff --git a/cmdline/mingw.c b/cmdline/mingw.c
index 1a4827b9..d82e36a8 100644
--- a/cmdline/mingw.c
+++ b/cmdline/mingw.c
@@ -173,6 +173,11 @@ void os_init(int opt)
 		SetThreadExecutionState(WIN32_ES_CONTINUOUS | WIN32_ES_SYSTEM_REQUIRED);
 	}
 
+	/* set stdout and stderr as "line buffered" */
+	/* this ensures that messages are mixed correctly */
+	setvbuf(stdout, 0, _IOLBF, BUFSIZ);
+	setvbuf(stderr, 0, _IOLBF, BUFSIZ);
+
 	last_error = 0;
 }
 
@@ -1907,7 +1912,6 @@ static void* thread_spinup(void* arg)
 
 	pthread_mutex_lock(&io_lock);
 	fprintf(stdout, "Spunup device '%" PRIx64 "' for disk '%s' in %" PRIu64 " ms.\n", (uint64_t)device, devinfo->name, tick_ms() - start);
-	fflush(stdout);
 	pthread_mutex_unlock(&io_lock);
 
 	return 0;
diff --git a/cmdline/parity.c b/cmdline/parity.c
index 838161bb..8009f77c 100644
--- a/cmdline/parity.c
+++ b/cmdline/parity.c
@@ -103,7 +103,7 @@ void parity_overflow(struct snapraid_state* state, data_off_t size)
 			if (file->blockmax > 0) {
 				if (file->blockvec[file->blockmax - 1].parity_pos >= blockalloc) {
 					ftag("outofparity:%s:%s\n", disk->name, file->sub);
-					fflush(stdlog);
+					fflush_log();
 					if (first) {
 						first = 0;
 						printf("\nYour data requires more parity than the available space.\n");
diff --git a/cmdline/pool.c b/cmdline/pool.c
index ae78ab5e..dcd43fb7 100644
--- a/cmdline/pool.c
+++ b/cmdline/pool.c
@@ -259,6 +259,6 @@ void state_pool(struct snapraid_state* state)
 
 	ftag("summary:link_count::%u\n", count);
 	ftag("summary:exit:ok\n");
-	fflush(stdlog);
+	fflush_log();
 }
 
diff --git a/cmdline/scan.c b/cmdline/scan.c
index ca1c84ce..44ac7ff8 100644
--- a/cmdline/scan.c
+++ b/cmdline/scan.c
@@ -1750,7 +1750,7 @@ void state_scan(struct snapraid_state* state, int is_diff)
 		} else {
 			ftag("summary:exit:diff\n");
 		}
-		fflush(stdlog);
+		fflush_log();
 	}
 
 	tommy_list_foreach(&scanlist, (tommy_foreach_func*)free);
diff --git a/cmdline/scrub.c b/cmdline/scrub.c
index 2844a331..643592dd 100644
--- a/cmdline/scrub.c
+++ b/cmdline/scrub.c
@@ -502,7 +502,7 @@ static int state_scrub_process(struct snapraid_state* state, struct snapraid_par
 		ftag("summary:exit:ok\n");
 	else
 		ftag("summary:exit:error\n");
-	fflush(stdlog);
+	fflush_log();
 
 bail:
 	for (j = 0; j < diskmax; ++j) {
diff --git a/cmdline/selftest.c b/cmdline/selftest.c
index 81b3b8d6..42485ec2 100644
--- a/cmdline/selftest.c
+++ b/cmdline/selftest.c
@@ -381,7 +381,7 @@ bail:
 void selftest(void)
 {
 	ftag("selftest:\n");
-	fflush(stdlog);
+	fflush_log();
 
 	printf("Self test...\n");
 
diff --git a/cmdline/snapraid.c b/cmdline/snapraid.c
index 49452865..1f333c52 100644
--- a/cmdline/snapraid.c
+++ b/cmdline/snapraid.c
@@ -924,7 +924,7 @@ int main(int argc, char* argv[])
 	ftag("command:%s\n", command);
 	for (i = 0; i < argc; ++i)
 		ftag("argv:%u:%s\n", i, argv[i]);
-	fflush(stdlog);
+	fflush_log();
 
 	if (!opt.skip_self)
 		selftest();
diff --git a/cmdline/state.c b/cmdline/state.c
index 1e1d2df6..a006bc89 100644
--- a/cmdline/state.c
+++ b/cmdline/state.c
@@ -930,7 +930,7 @@ void state_config(struct snapraid_state* state, const char* path, const char* co
 	if (state->filter_hidden)
 		ftag("filter:nohidden:\n");
 
-	fflush(stdlog);
+	fflush_log();
 }
 
 /**
@@ -4284,7 +4284,7 @@ void state_read(struct snapraid_state* state)
 
 		if (!state->no_conf) {
 			ftag("content:%s\n", path);
-			fflush(stdlog);
+			fflush_log();
 		}
 		printf("Loading state from %s...\n", path);
 
@@ -4593,7 +4593,7 @@ int state_progress_begin(struct snapraid_state* state, block_off_t blockstart, b
 
 	if (state->opt.gui) {
 		ftag("run:begin:%u:%u:%u\n", blockstart, blockmax, countmax);
-		fflush(stdlog);
+		fflush_log();
 	}
 
 	now = time(0);
@@ -4611,7 +4611,7 @@ int state_progress_begin(struct snapraid_state* state, block_off_t blockstart, b
 			printf("Not starting for interruption\n");
 		}
 		ftag("sigint:0: SIGINT received\n");
-		fflush(stdlog);
+		fflush_log();
 		return 0;
 		/* LCOV_EXCL_STOP */
 	}
@@ -4623,7 +4623,7 @@ void state_progress_end(struct snapraid_state* state, block_off_t countpos, bloc
 {
 	if (state->opt.gui) {
 		ftag("run:end\n");
-		fflush(stdlog);
+		fflush_log();
 	} else {
 		time_t now;
 		time_t elapsed;
@@ -4758,7 +4758,7 @@ int state_progress(struct snapraid_state* state, block_off_t blockpos, block_off
 
 		if (state->opt.gui) {
 			ftag("run:pos:%u:%u:%" PRIu64 ":%u:%u:%u:%u:%" PRIu64 "\n", blockpos, countpos, countsize, out_perc, out_eta, out_speed, out_cpu, (uint64_t)elapsed);
-			fflush(stdlog);
+			fflush_log();
 		} else {
 			printf("%u%%, %u MiB", out_perc, (unsigned)(countsize / (1024 * 1024)));
 			if (out_speed)
@@ -4795,7 +4795,7 @@ int state_progress(struct snapraid_state* state, block_off_t blockpos, block_off
 			printf("Stopping for interruption at block %u\n", blockpos);
 		}
 		ftag("sigint:%u: SIGINT received\n", blockpos);
-		fflush(stdlog);
+		fflush_log();
 		return 1;
 		/* LCOV_EXCL_STOP */
 	}
diff --git a/cmdline/status.c b/cmdline/status.c
index 0e8e2cac..8d280ef7 100644
--- a/cmdline/status.c
+++ b/cmdline/status.c
@@ -242,7 +242,7 @@ int state_status(struct snapraid_state* state)
 	ftag("summary:hash:%s\n", hash_config_name(state->hash));
 	ftag("summary:prev_hash:%s\n", hash_config_name(state->prevhash));
 	ftag("summary:best_hash:%s\n", hash_config_name(state->besthash));
-	fflush(stdlog);
+	fflush_log();
 
 	/* copy the info a temp vector, and count bad/rehash/unsynced blocks */
 	infomap = malloc_nofail(blockmax * sizeof(snapraid_info));
@@ -303,7 +303,7 @@ int state_status(struct snapraid_state* state)
 	ftag("summary:has_unsynced:%u\n", unsynced_blocks);
 	ftag("summary:has_rehash:%u\n", rehash);
 	ftag("summary:has_bad:%u:%u:%u\n", bad, bad_first, bad_last);
-	fflush(stdlog);
+	fflush_log();
 
 	if (!count) {
 		ferr("The array is empty.\n");
diff --git a/cmdline/support.c b/cmdline/support.c
index 1ebd95fb..a2420108 100644
--- a/cmdline/support.c
+++ b/cmdline/support.c
@@ -63,6 +63,12 @@ void flog(const char* format, ...)
 	}
 }
 
+void fflush_log(void)
+{
+	if (stdlog)
+		fflush(stdlog);
+}
+
 void ftag(const char* format, ...)
 {
 	va_list ap;
diff --git a/cmdline/support.h b/cmdline/support.h
index c79bfbdf..0c7f6085 100644
--- a/cmdline/support.h
+++ b/cmdline/support.h
@@ -48,6 +48,11 @@ void ferr(const char* format, ...) __attribute__((format(printf, 1, 2)));
  */
 void flog(const char* format, ...) __attribute__((format(printf, 1, 2)));
 
+/**
+ * Flush the log output.
+ */
+void fflush_log(void);
+
 /**
  * Tag message.
  *
diff --git a/cmdline/sync.c b/cmdline/sync.c
index 60f468ca..2283ab35 100644
--- a/cmdline/sync.c
+++ b/cmdline/sync.c
@@ -1151,7 +1151,7 @@ end:
 		ftag("summary:exit:ok\n");
 	else
 		ftag("summary:exit:error\n");
-	fflush(stdlog);
+	fflush_log();
 
 bail:
 	for (j = 0; j < diskmax; ++j) {
diff --git a/cmdline/unix.c b/cmdline/unix.c
index 0d995a7b..47f94f9a 100644
--- a/cmdline/unix.c
+++ b/cmdline/unix.c
@@ -957,6 +957,11 @@ int devquery(tommy_list* high, tommy_list* low, int operation)
 void os_init(int opt)
 {
 	(void)opt;
+
+	/* set stdout and stderr as "line buffered" */
+	/* this ensures that messages are mixed correctly */
+	setvbuf(stdout, 0, _IOLBF, BUFSIZ);
+	setvbuf(stderr, 0, _IOLBF, BUFSIZ);
 }
 
 void os_done(void)