diff --git a/src/autoload.cpp b/src/autoload.cpp
index 46e36ac57..39cd3b515 100644
--- a/src/autoload.cpp
+++ b/src/autoload.cpp
@@ -25,7 +25,7 @@
 static const int kAutoloadStalenessInterval = 15;
 
 file_access_attempt_t access_file(const wcstring &path, int mode) {
-    // wprintf(L"Touch %ls\n", path.c_str());
+    // fwprintf(stderr, L"Touch %ls\n", path.c_str());
     file_access_attempt_t result = {};
     struct stat statbuf;
     if (wstat(path, &statbuf)) {
diff --git a/src/common.cpp b/src/common.cpp
index 0cfd6959e..c804d4909 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -608,7 +608,7 @@ void debug_safe(int level, const char *msg, const char *param1, const char *para
                                   param7, param8, param9, param10, param11, param12};
     if (!msg) return;
 
-    // Can't call wprintf, that may allocate memory Just call write() over and over.
+    // Can't call fwprintf, that may allocate memory Just call write() over and over.
     if (level > debug_level) return;
     int errno_old = errno;
 
@@ -1691,7 +1691,7 @@ bool is_forked_child(void) {
 
     bool is_child_of_fork = (getpid() != initial_pid);
     if (is_child_of_fork) {
-        wprintf(L"Uh-oh: %d\n", getpid());
+        debug(0, L"Uh-oh: getpid() != initial_pid: %d != %d\n", getpid(), initial_pid);
         while (1) sleep(10000);
     }
     return is_child_of_fork;
diff --git a/src/event.cpp b/src/event.cpp
index 71f811437..e365f5dfa 100644
--- a/src/event.cpp
+++ b/src/event.cpp
@@ -162,11 +162,11 @@ wcstring event_get_desc(const event_t &e) {
 
 #if 0
 static void show_all_handlers(void) {
-    wprintf(L"event handlers:\n");
+    fwprintf(stdout, L"event handlers:\n");
     for (event_list_t::const_iterator iter = events.begin(); iter != events.end(); ++iter) {
         const event_t *foo = *iter;
         wcstring tmp = event_get_desc(foo);
-        wprintf(L"    handler now %ls\n", tmp.c_str());
+        fwprintf(stdout, L"    handler now %ls\n", tmp.c_str());
     }
 }
 #endif
diff --git a/src/expand.cpp b/src/expand.cpp
index 2004f8970..2ea9459db 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -763,7 +763,7 @@ static int expand_variables(const wcstring &instr, std::vector<completion_t> *ou
             stop_pos++;
         }
 
-        // wprintf(L"Stop for '%c'\n", in[stop_pos]);
+        // fwprintf(stdout, L"Stop for '%c'\n", in[stop_pos]);
         var_len = stop_pos - start_pos;
 
         if (var_len == 0) {
diff --git a/src/fish_key_reader.cpp b/src/fish_key_reader.cpp
index c3a6380b8..b850cbd28 100644
--- a/src/fish_key_reader.cpp
+++ b/src/fish_key_reader.cpp
@@ -183,7 +183,7 @@ static void output_info_about_char(wchar_t wc) {
 static bool output_matching_key_name(wchar_t wc) {
     char *name = sequence_name(wc);
     if (name) {
-        wprintf(L"bind -k %s 'do something'\n", name);
+        fwprintf(stdout, L"bind -k %s 'do something'\n", name);
         free(name);
         return true;
     }
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index ac038e0bd..50eaa9886 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -100,9 +100,9 @@ static int err_count = 0;
 static void say(const wchar_t *fmt, ...) {
     va_list va;
     va_start(va, fmt);
-    vwprintf(fmt, va);
+    vfwprintf(stdout, fmt, va);
     va_end(va);
-    wprintf(L"\n");
+    fwprintf(stdout, L"\n");
 }
 
 /// Print formatted error string.
@@ -118,8 +118,8 @@ static void err(const wchar_t *blah, ...) {
     if (colorize) {
         fputws(L"\e[31m", stdout);
     }
-    wprintf(L"Error: ");
-    vwprintf(blah, va);
+    fwprintf(stdout, L"Error: ");
+    vfwprintf(stdout, blah, va);
     va_end(va);
 
     // Return to normal color.
@@ -127,7 +127,7 @@ static void err(const wchar_t *blah, ...) {
         fputws(L"\e[0m", stdout);
     }
 
-    wprintf(L"\n");
+    fwprintf(stdout, L"\n");
 }
 
 /// Joins a wcstring_list_t via commas.
@@ -451,8 +451,8 @@ static void test_tokenizer() {
             }
             if (types[i] != token.type) {
                 err(L"Tokenization error:");
-                wprintf(L"Token number %zu of string \n'%ls'\n, got token type %ld\n", i + 1, str,
-                        (long)token.type);
+                fwprintf(stdout, L"Token number %zu of string \n'%ls'\n, got token type %ld\n",
+                         i + 1, str, (long)token.type);
             }
             i++;
         }
@@ -1726,7 +1726,8 @@ static void test_1_word_motion(word_motion_t motion, move_word_style_t style,
         size_t char_idx = (motion == word_motion_left ? idx - 1 : idx);
         wchar_t wc = command.at(char_idx);
         bool will_stop = !sm.consume_char(wc);
-        // wprintf(L"idx %lu, looking at %lu (%c): %d\n", idx, char_idx, (char)wc, will_stop);
+        // fwprintf(stdout, L"idx %lu, looking at %lu (%c): %d\n", idx, char_idx, (char)wc,
+        //          will_stop);
         bool expected_stop = (stops.count(idx) > 0);
         if (will_stop != expected_stop) {
             wcstring tmp = command;
@@ -2211,15 +2212,15 @@ static void perform_one_autosuggestion_cd_test(const wcstring &command,
     bool expects_error = (expected == L"<error>");
 
     if (comps.empty() && !expects_error) {
-        printf("line %ld: autosuggest_suggest_special() failed for command %ls\n", line,
-               command.c_str());
+        fwprintf(stderr, L"line %ld: autosuggest_suggest_special() failed for command %ls\n", line,
+                 command.c_str());
         do_test(!comps.empty());
         return;
     } else if (!comps.empty() && expects_error) {
-        printf(
-            "line %ld: autosuggest_suggest_special() was expected to fail but did not, for command "
-            "%ls\n",
-            line, command.c_str());
+        fwprintf(stderr,
+                 L"line %ld: autosuggest_suggest_special() was expected to fail but did not, "
+                 L"for command %ls\n",
+                 line, command.c_str());
         do_test(comps.empty());
     }
 
@@ -2228,11 +2229,12 @@ static void perform_one_autosuggestion_cd_test(const wcstring &command,
         const completion_t &suggestion = comps.at(0);
 
         if (suggestion.completion != expected) {
-            printf(
-                "line %ld: complete() for cd returned the wrong expected string for command %ls\n",
+            fwprintf(
+                stderr,
+                L"line %ld: complete() for cd returned the wrong expected string for command %ls\n",
                 line, command.c_str());
-            printf("  actual: %ls\n", suggestion.completion.c_str());
-            printf("expected: %ls\n", expected.c_str());
+            fwprintf(stderr, L"  actual: %ls\n", suggestion.completion.c_str());
+            fwprintf(stderr, L"expected: %ls\n", expected.c_str());
             do_test(suggestion.completion == expected);
         }
     }
@@ -2347,8 +2349,9 @@ static void perform_one_autosuggestion_should_ignore_test(const wcstring &comman
     do_test(comps.empty());
     if (!comps.empty()) {
         const wcstring &suggestion = comps.front().completion;
-        printf("line %ld: complete() expected to return nothing for %ls\n", line, command.c_str());
-        printf("  instead got: %ls\n", suggestion.c_str());
+        fwprintf(stderr, L"line %ld: complete() expected to return nothing for %ls\n", line,
+                 command.c_str());
+        fwprintf(stderr, L"  instead got: %ls\n", suggestion.c_str());
     }
 }
 
@@ -3136,7 +3139,7 @@ void history_tests_t::test_history_speed(void)
         if (stop >= end)
             break;
     }
-    printf("%lu items - %.2f msec per item\n", (unsigned long)count, (stop - start) * 1E6 / count);
+    fwprintf(stdout, L"%lu items - %.2f msec per item\n", (unsigned long)count, (stop - start) * 1E6 / count);
     hist->clear();
     delete hist;
 }
diff --git a/src/iothread.cpp b/src/iothread.cpp
index eb55f8da5..10002640b 100644
--- a/src/iothread.cpp
+++ b/src/iothread.cpp
@@ -275,7 +275,8 @@ void iothread_drain_all(void) {
     }
 #if TIME_DRAIN
     double after = timef();
-    wprintf(L"(Waited %.02f msec for %d thread(s) to drain)\n", 1000 * (after - now), thread_count);
+    fwprintf(stdout, L"(Waited %.02f msec for %d thread(s) to drain)\n", 1000 * (after - now),
+             thread_count);
 #endif
 }
 
diff --git a/src/output.cpp b/src/output.cpp
index 1716597ea..b4bb9f71e 100644
--- a/src/output.cpp
+++ b/src/output.cpp
@@ -537,8 +537,8 @@ rgb_color_t parse_color(const wcstring &val, bool is_background) {
 
 #if 0
     wcstring desc = result.description();
-    wprintf(L"Parsed %ls from %ls (%s)\n", desc.c_str(), val.c_str(),
-           is_background ? "background" : "foreground");
+    fwprintf(stdout, L"Parsed %ls from %ls (%s)\n", desc.c_str(), val.c_str(),
+             is_background ? "background" : "foreground");
 #endif
 
     return result;
diff --git a/src/proc.cpp b/src/proc.cpp
index 116d1d116..0237145bb 100644
--- a/src/proc.cpp
+++ b/src/proc.cpp
@@ -80,9 +80,9 @@ void print_jobs(void)
     job_iterator_t jobs;
     job_t *j;
     while (j = jobs.next()) {
-        wprintf("%p -> %ls -> (foreground %d, complete %d, stopped %d, constructed %d)\n",
-                j, j->command_wcstr(), job_get_flag(j, JOB_FOREGROUND), job_is_completed(j),
-                job_is_stopped(j), job_get_flag(j, JOB_CONSTRUCTED));
+        fwprintf(stdout, L"%p -> %ls -> (foreground %d, complete %d, stopped %d, constructed %d)\n",
+                 j, j->command_wcstr(), job_get_flag(j, JOB_FOREGROUND), job_is_completed(j),
+                 job_is_stopped(j), job_get_flag(j, JOB_CONSTRUCTED));
     }
 }
 #endif
@@ -944,7 +944,7 @@ void job_continue(job_t *j, bool cont) {
             // and it is not a short circuited builtin.
             if ((WIFEXITED(p->status) || WIFSIGNALED(p->status)) && p->pid) {
                 int status = proc_format_status(p->status);
-                // wprintf(L"setting status %d for %ls\n", job_get_flag( j, JOB_NEGATE
+                // fwprintf(stdout, L"setting status %d for %ls\n", job_get_flag( j, JOB_NEGATE
                 // )?!status:status, j->command);
                 proc_set_last_status(job_get_flag(j, JOB_NEGATE) ? !status : status);
             }
diff --git a/src/screen.cpp b/src/screen.cpp
index ed88745d7..d40bdcb1a 100644
--- a/src/screen.cpp
+++ b/src/screen.cpp
@@ -661,7 +661,7 @@ static bool test_stuff(screen_t *scr)
         int c = getchar();
         if (c != EOF) break;
     }
-    wprintf(L"Bye\n");
+    fwprintf(stdout, L"Bye\n");
     exit(0);
     while (1) sleep(10000);
     return true;
diff --git a/src/tokenizer.cpp b/src/tokenizer.cpp
index 0bbfd84ef..126269940 100644
--- a/src/tokenizer.cpp
+++ b/src/tokenizer.cpp
@@ -489,7 +489,7 @@ void tokenizer_t::tok_next() {
     }
 
     if (!this->has_next) {
-        // wprintf( L"EOL\n" );
+        // fwprintf(stdout, L"EOL\n" );
         this->last_type = TOK_END;
         return;
     }
@@ -666,7 +666,7 @@ bool move_word_state_machine_t::consume_char_path_components(wchar_t c) {
         s_end
     };
 
-    // wprintf(L"state %d, consume '%lc'\n", state, c);
+    // fwprintf(stdout, L"state %d, consume '%lc'\n", state, c);
     bool consumed = false;
     while (state != s_end && !consumed) {
         switch (state) {