diff --git a/src/x11_init.c b/src/x11_init.c
index 57207025..f9c56675 100644
--- a/src/x11_init.c
+++ b/src/x11_init.c
@@ -366,7 +366,7 @@ static void createKeyTables(void)
             // keyboard layout. Because function keys aren't mapped correctly
             // when using traditional KeySym translations, they are mapped
             // here instead.
-            for (int i = 0;  i < sizeof(keymap) / sizeof(keymap[0]);  i++)
+            for (size_t i = 0;  i < sizeof(keymap) / sizeof(keymap[0]);  i++)
             {
                 if (strncmp(desc->names->keys[scancode].name,
                             keymap[i].name,
@@ -390,7 +390,7 @@ static void createKeyTables(void)
                     continue;
                 }
 
-                for (int j = 0;  j < sizeof(keymap) / sizeof(keymap[0]);  j++)
+                for (size_t j = 0;  j < sizeof(keymap) / sizeof(keymap[0]);  j++)
                 {
                     if (strncmp(desc->names->key_aliases[i].alias,
                                 keymap[j].name,
diff --git a/src/x11_monitor.c b/src/x11_monitor.c
index 38af7e0c..404d766f 100644
--- a/src/x11_monitor.c
+++ b/src/x11_monitor.c
@@ -179,8 +179,8 @@ void _glfwPollMonitorsX11(void)
             {
                 if (screens[j].x_org == ci->x &&
                     screens[j].y_org == ci->y &&
-                    screens[j].width == ci->width &&
-                    screens[j].height == ci->height)
+                    screens[j].width == (int)ci->width &&
+                    screens[j].height == (int)ci->height)
                 {
                     monitor->x11.index = j;
                     break;
@@ -572,7 +572,7 @@ void _glfwSetGammaRampX11(_GLFWmonitor* monitor, const GLFWgammaramp* ramp)
 {
     if (_glfw.x11.randr.available && !_glfw.x11.randr.gammaBroken)
     {
-        if (XRRGetCrtcGammaSize(_glfw.x11.display, monitor->x11.crtc) != ramp->size)
+        if (XRRGetCrtcGammaSize(_glfw.x11.display, monitor->x11.crtc) != (int)ramp->size)
         {
             _glfwInputError(GLFW_PLATFORM_ERROR,
                             "X11: Gamma ramp size must match current ramp size");
diff --git a/src/x11_window.c b/src/x11_window.c
index b69755d1..2f8735d2 100644
--- a/src/x11_window.c
+++ b/src/x11_window.c
@@ -97,7 +97,7 @@ static GLFWbool waitForAnyEvent(double* timeout)
         if (!_glfwPollPOSIX(fds, sizeof(fds) / sizeof(fds[0]), timeout))
             return GLFW_FALSE;
 
-        for (int i = 1; i < sizeof(fds) / sizeof(fds[0]); i++)
+        for (size_t i = 1; i < sizeof(fds) / sizeof(fds[0]); i++)
         {
             if (fds[i].revents & POLLIN)
                 return GLFW_TRUE;
@@ -235,10 +235,10 @@ static int translateState(int state)
 
 // Translates an X11 key code to a GLFW key token
 //
-static int translateKey(int scancode)
+static int translateKey(unsigned int scancode)
 {
     // Use the pre-filled LUT (see createKeyTables() in x11_init.c)
-    if (scancode < 0 || scancode > 255)
+    if (scancode > 255)
         return GLFW_KEY_UNKNOWN;
 
     return _glfw.x11.keycodes[scancode];
@@ -1145,7 +1145,7 @@ static void releaseMonitor(_GLFWwindow* window)
 //
 static void processEvent(XEvent *event)
 {
-    int keycode = 0;
+    unsigned int keycode = 0;
     Bool filtered = False;
 
     // HACK: Save scancode as some IMs clear the field in XFilterEvent