diff --git a/helpers/auth_x11.c b/helpers/auth_x11.c
index 5d6ff087..e9b2308a 100644
--- a/helpers/auth_x11.c
+++ b/helpers/auth_x11.c
@@ -455,8 +455,7 @@ const char *GetIndicators(int *warning, int *have_multiple_layouts) {
     have_output = 1;
   }
 
-  int i;
-  for (i = 0; i < XkbNumIndicators; i++) {
+  for (int i = 0; i < XkbNumIndicators; i++) {
     if (!(istate & (1U << i))) {
       continue;
     }
@@ -495,8 +494,7 @@ const char *GetIndicators(int *warning, int *have_multiple_layouts) {
 }
 
 void DestroyPerMonitorWindows(size_t keep_windows) {
-  size_t i;
-  for (i = keep_windows; i < num_windows; ++i) {
+  for (size_t i = keep_windows; i < num_windows; ++i) {
 #ifdef HAVE_XFT_EXT
     XftDrawDestroy(xft_draws[i]);
 #endif
@@ -618,8 +616,7 @@ void UpdatePerMonitorWindows(int monitors_changed, int region_w, int region_h,
     unsigned int unused_mask;
     XQueryPointer(display, parent_window, &unused_root, &unused_child,
                   &unused_root_x, &unused_root_y, &x, &y, &unused_mask);
-    size_t i;
-    for (i = 0; i < num_monitors; ++i) {
+    for (size_t i = 0; i < num_monitors; ++i) {
       if (x >= monitors[i].x && x < monitors[i].x + monitors[i].width &&
           y >= monitors[i].y && y < monitors[i].y + monitors[i].height) {
         CreateOrUpdatePerMonitorWindow(0, &monitors[i], region_w, region_h,
@@ -641,8 +638,7 @@ void UpdatePerMonitorWindows(int monitors_changed, int region_w, int region_h,
   size_t new_num_windows = num_monitors;
 
   // Update or create everything.
-  size_t i;
-  for (i = 0; i < new_num_windows; ++i) {
+  for (size_t i = 0; i < new_num_windows; ++i) {
     CreateOrUpdatePerMonitorWindow(i, &monitors[i], region_w, region_h,
                                    x_offset, y_offset);
   }
@@ -875,8 +871,7 @@ void DisplayMessage(const char *title, const char *str, int is_warning) {
                           x_offset, y_offset);
   per_monitor_windows_dirty = 0;
 
-  size_t i;
-  for (i = 0; i < num_windows; ++i) {
+  for (size_t i = 0; i < num_windows; ++i) {
     int cx = region_w / 2;
     int cy = region_h / 2;
     int y = cy + to - box_h / 2;
@@ -1095,8 +1090,8 @@ int Prompt(const char *msg, char **response, int echo) {
               stride * DISCO_PASSWORD_DANCERS * strlen(disco_dancers[0]) +
               strlen(disco_combiner);
 
-          size_t i, bit;
-          for (i = 0, bit = 1; i < DISCO_PASSWORD_DANCERS; ++i, bit <<= 1) {
+          for (size_t i = 0, bit = 1; i < DISCO_PASSWORD_DANCERS;
+               ++i, bit <<= 1) {
             const char *dancer =
                 disco_dancers[(priv.displaymarker & bit) ? 1 : 0];
             memcpy(priv.displaybuf + i * stride, disco_combiner,
@@ -1468,8 +1463,8 @@ enum PasswordPrompt GetPasswordPromptFromFlags(
                                   : PASSWORD_PROMPT_ASTERISKS;
   }
 
-  enum PasswordPrompt prompt;
-  for (prompt = 0; prompt < PASSWORD_PROMPT_COUNT; ++prompt) {
+  for (enum PasswordPrompt prompt = 0; prompt < PASSWORD_PROMPT_COUNT;
+       ++prompt) {
     if (strcmp(password_prompt_flag, PasswordPromptStrings[prompt]) == 0) {
       return prompt;
     }
diff --git a/helpers/authproto_pam.c b/helpers/authproto_pam.c
index de35730a..5ec575f5 100644
--- a/helpers/authproto_pam.c
+++ b/helpers/authproto_pam.c
@@ -84,15 +84,14 @@ int Converse(int num_msg, const struct pam_message **msg,
 
   *resp = calloc(num_msg, sizeof(struct pam_response));
 
-  int i;
-  for (i = 0; i < num_msg; ++i) {
+  for (int i = 0; i < num_msg; ++i) {
     int status = ConverseOne(msg[i], &(*resp)[i]);
     if (status != PAM_SUCCESS) {
-      for (i = 0; i < num_msg; ++i) {
-        if ((*resp)[i].resp != NULL) {
-          explicit_bzero((*resp)[i].resp, strlen((*resp)[i].resp));
+      for (int j = 0; j < num_msg; ++j) {
+        if ((*resp)[j].resp != NULL) {
+          explicit_bzero((*resp)[j].resp, strlen((*resp)[j].resp));
         }
-        free((*resp)[i].resp);
+        free((*resp)[j].resp);
       }
       free(*resp);
       *resp = NULL;
diff --git a/helpers/dimmer.c b/helpers/dimmer.c
index 43129ce7..be0a8ed2 100644
--- a/helpers/dimmer.c
+++ b/helpers/dimmer.c
@@ -157,8 +157,7 @@ void DitherEffectDrawFrame(void *self, Display *display, Window dim_window,
   int start_pframe = frame * dimmer->pattern_frames / dimmer->super.frame_count;
   int end_pframe =
       (frame + 1) * dimmer->pattern_frames / dimmer->super.frame_count;
-  int pframe;
-  for (pframe = start_pframe; pframe < end_pframe; ++pframe) {
+  for (int pframe = start_pframe; pframe < end_pframe; ++pframe) {
     int x, y;
     Bayer(pframe, dimmer->pattern_power, &x, &y);
     XDrawPoint(display, dimmer->pattern, dimmer->pattern_gc, x, y);
@@ -168,13 +167,12 @@ void DitherEffectDrawFrame(void *self, Display *display, Window dim_window,
   XChangeGC(display, dimmer->dim_gc, GCStipple, &dimmer->gc_values);
   // But do it in some sub-rectangles to be easier on the X server on large
   // screens.
-  int x, y;
-  for (y = 0; y < h; y += dimmer->max_fill_size) {
+  for (int y = 0; y < h; y += dimmer->max_fill_size) {
     int hh = h - y;
     if (hh > dimmer->max_fill_size) {
       hh = dimmer->max_fill_size;
     }
-    for (x = 0; x < w; x += dimmer->max_fill_size) {
+    for (int x = 0; x < w; x += dimmer->max_fill_size) {
       int ww = w - x;
       if (ww > dimmer->max_fill_size) {
         ww = dimmer->max_fill_size;
@@ -376,8 +374,7 @@ int main(int argc, char **argv) {
   sleep_ts.tv_sec = sleep_time_ns / 1000000000;
   sleep_ts.tv_nsec = sleep_time_ns % 1000000000;
   XMapRaised(display, dim_window);
-  int i;
-  for (i = 0; i < dimmer->frame_count; ++i) {
+  for (int i = 0; i < dimmer->frame_count; ++i) {
     // Advance the dim pattern by one step.
     dimmer->DrawFrame(dimmer, display, dim_window, i, w, h);
     // Sleep a while. Yes, even at the end now - we want the user to see this
diff --git a/helpers/monitors.c b/helpers/monitors.c
index c099b539..4227f548 100644
--- a/helpers/monitors.c
+++ b/helpers/monitors.c
@@ -111,8 +111,7 @@ static void AddMonitor(Monitor* out_monitors, size_t* num_monitors,
     return;
   }
   // Skip overlapping "monitors" (typically in cloned display setups).
-  size_t i;
-  for (i = 0; i < *num_monitors; ++i) {
+  for (size_t i = 0; i < *num_monitors; ++i) {
     if (IntervalsOverlap(x, w, out_monitors[i].x, out_monitors[i].width) &&
         IntervalsOverlap(y, h, out_monitors[i].y, out_monitors[i].height)) {
 #ifdef DEBUG_EVENTS
@@ -139,8 +138,7 @@ static int GetMonitorsXRandR12(Display* dpy, Window window, int wx, int wy,
   if (screenres == NULL) {
     return 0;
   }
-  int i;
-  for (i = 0; i < screenres->noutput; ++i) {
+  for (int i = 0; i < screenres->noutput; ++i) {
     XRROutputInfo* output =
         XRRGetOutputInfo(dpy, screenres, screenres->outputs[i]);
     if (output == NULL) {
@@ -182,8 +180,7 @@ static int GetMonitorsXRandR15(Display* dpy, Window window, int wx, int wy,
   if (rrmonitors == NULL) {
     return 0;
   }
-  int i;
-  for (i = 0; i < num_rrmonitors; ++i) {
+  for (int i = 0; i < num_rrmonitors; ++i) {
     XRRMonitorInfo* info = &rrmonitors[i];
     int x = CLAMP(info->x, wx, wx + ww) - wx;
     int y = CLAMP(info->y, wy, wy + wh) - wy;
@@ -233,8 +230,7 @@ static void GetMonitorsGuess(const XWindowAttributes* xwa,
   size_t guessed_monitors = CLAMP((size_t)(xwa->width * 9 + xwa->height * 8) /
                                       (size_t)(xwa->height * 16),  //
                                   1, max_monitors);
-  size_t i;
-  for (i = 0; i < guessed_monitors; ++i) {
+  for (size_t i = 0; i < guessed_monitors; ++i) {
     int x = xwa->width * i / guessed_monitors;
     int y = 0;
     int w = (xwa->width * (i + 1) / guessed_monitors) -
diff --git a/helpers/saver_multiplex.c b/helpers/saver_multiplex.c
index fb60eccb..95271847 100644
--- a/helpers/saver_multiplex.c
+++ b/helpers/saver_multiplex.c
@@ -50,8 +50,7 @@ static size_t num_monitors;
 static Window windows[MAX_MONITORS];
 
 static void WatchSavers(void) {
-  size_t i;
-  for (i = 0; i < num_monitors; ++i) {
+  for (size_t i = 0; i < num_monitors; ++i) {
     WatchSaverChild(display, windows[i], i, saver_executable, 1);
   }
 }
@@ -59,8 +58,7 @@ static void WatchSavers(void) {
 static void SpawnSavers(Window parent, int argc, char* const* argv) {
   XSetWindowAttributes attrs = {0};
   attrs.background_pixel = BlackPixel(display, DefaultScreen(display));
-  size_t i;
-  for (i = 0; i < num_monitors; ++i) {
+  for (size_t i = 0; i < num_monitors; ++i) {
     windows[i] =
         XCreateWindow(display, parent, monitors[i].x, monitors[i].y,
                       monitors[i].width, monitors[i].height, 0, CopyFromParent,
@@ -75,8 +73,7 @@ static void SpawnSavers(Window parent, int argc, char* const* argv) {
 }
 
 static void KillSavers(void) {
-  size_t i;
-  for (i = 0; i < num_monitors; ++i) {
+  for (size_t i = 0; i < num_monitors; ++i) {
     WatchSaverChild(display, windows[i], i, saver_executable, 0);
     XDestroyWindow(display, windows[i]);
   }
diff --git a/helpers/until_nonidle.c b/helpers/until_nonidle.c
index a288e78d..fae69561 100644
--- a/helpers/until_nonidle.c
+++ b/helpers/until_nonidle.c
@@ -81,8 +81,7 @@ uint64_t GetIdleTimeForSingleTimer(Display *display, Window w,
   } else {
 #ifdef HAVE_XSYNC_EXT
     if (have_xsync_ext) {
-      int i;
-      for (i = 0; i < num_xsync_counters; ++i) {
+      for (int i = 0; i < num_xsync_counters; ++i) {
         if (!strcmp(timer,
                     xsync_counters[i].name)) {  // I know this is inefficient.
           XSyncValue value;
diff --git a/main.c b/main.c
index b505c0bc..d9e90334 100644
--- a/main.c
+++ b/main.c
@@ -441,8 +441,7 @@ void LoadDefaults() {
  * Possible errors will be printed on stderr.
  */
 void ParseArgumentsOrExit(int argc, char **argv) {
-  int i;
-  for (i = 1; i < argc; ++i) {
+  for (int i = 1; i < argc; ++i) {
     if (!strncmp(argv[i], "auth_", 5)) {
       Log("Setting auth child name from command line is DEPRECATED. Use "
           "the XSECURELOCK_AUTH environment variable instead");
@@ -983,8 +982,8 @@ int main(int argc, char **argv) {
         XIMPreeditNone | XIMStatusNothing,     // Status might be invisible.
         XIMPreeditNone | XIMStatusNone         // Standard handling.
     };
-    size_t i;
-    for (i = 0; i < sizeof(input_styles) / sizeof(input_styles[0]); ++i) {
+    for (size_t i = 0; i < sizeof(input_styles) / sizeof(input_styles[0]);
+         ++i) {
       // Note: we draw XIM stuff in auth_window so it's above the saver/auth
       // child. However, we receive events for the grab window.
       xic = XCreateIC(xim, XNInputStyle, input_styles[i], XNClientWindow,
@@ -1020,11 +1019,11 @@ int main(int argc, char **argv) {
 
   // Acquire all grabs we need. Retry in case the window manager is still
   // holding some grabs while starting XSecureLock.
-  int retries;
   int last_normal_attempt = force_grab ? 1 : 0;
   Window previous_focused_window = None;
   int previous_revert_focus_to = RevertToNone;
-  for (retries = 10; retries >= 0; --retries) {
+  int retries = 10;
+  for (; retries >= 0; --retries) {
     if (AcquireGrabs(display, root_window, my_windows, n_my_windows,
                      transparent_cursor,
                      /*silent=*/retries > last_normal_attempt,
diff --git a/saver_child.c b/saver_child.c
index 983f7478..d96cd2ca 100644
--- a/saver_child.c
+++ b/saver_child.c
@@ -30,8 +30,7 @@ static pid_t saver_child_pid[MAX_SAVERS] = {0};
 void KillAllSaverChildrenSigHandler(int signo) {
   // This is a signal handler, so we're not going to make this too
   // complicated. Just kill 'em all.
-  int i;
-  for (i = 0; i < MAX_SAVERS; ++i) {
+  for (int i = 0; i < MAX_SAVERS; ++i) {
     if (saver_child_pid[i] != 0) {
       KillPgrp(saver_child_pid[i], signo);
     }
diff --git a/unmap_all.c b/unmap_all.c
index db3a91cf..ed0d1c22 100644
--- a/unmap_all.c
+++ b/unmap_all.c
@@ -21,8 +21,7 @@ int InitUnmapAllWindowsState(UnmapAllWindowsState* state, Display* display,
   XQueryTree(state->display, state->root_window, &unused_root_return,
              &unused_parent_return, &state->windows, &state->n_windows);
   state->first_unmapped_window = state->n_windows;  // That means none unmapped.
-  unsigned int i;
-  for (i = 0; i < state->n_windows; ++i) {
+  for (unsigned int i = 0; i < state->n_windows; ++i) {
     XWindowAttributes xwa;
     XGetWindowAttributes(display, state->windows[i], &xwa);
     // Not mapped -> nothing to do.
@@ -36,8 +35,7 @@ int InitUnmapAllWindowsState(UnmapAllWindowsState* state, Display* display,
       state->windows[i] = XmuClientWindow(display, state->windows[i]);
     }
     // If any window we'd be unmapping is in the ignore list, skip it.
-    unsigned int j;
-    for (j = 0; j < n_ignored_windows; ++j) {
+    for (unsigned int j = 0; j < n_ignored_windows; ++j) {
       if (state->windows[i] == ignored_windows[j]) {
         state->windows[i] = None;
       }
@@ -76,8 +74,8 @@ int UnmapAllWindows(UnmapAllWindowsState* state,
   if (state->first_unmapped_window == 0) {  // Already all unmapped.
     return 0;
   }
-  unsigned int i;
-  for (i = state->first_unmapped_window - 1;; --i) {  // Top-to-bottom order!
+  for (unsigned int i = state->first_unmapped_window - 1;;
+       --i) {  // Top-to-bottom order!
     if (state->windows[i] != None) {
       XUnmapWindow(state->display, state->windows[i]);
       state->first_unmapped_window = i;
@@ -94,8 +92,8 @@ int UnmapAllWindows(UnmapAllWindowsState* state,
 }
 
 void RemapAllWindows(UnmapAllWindowsState* state) {
-  unsigned int i;
-  for (i = state->first_unmapped_window; i < state->n_windows; ++i) {
+  for (unsigned int i = state->first_unmapped_window; i < state->n_windows;
+       ++i) {
     if (state->windows[i] != None) {
       XMapWindow(state->display, state->windows[i]);
     }