diff --git a/src/geometry/glyph_atlas.cpp b/src/geometry/glyph_atlas.cpp
index 50524f018..9e74e21b2 100644
--- a/src/geometry/glyph_atlas.cpp
+++ b/src/geometry/glyph_atlas.cpp
@@ -122,10 +122,36 @@ void GlyphAtlas::removeGlyphs(uint64_t tile_id) {
 
 void GlyphAtlas::upload() {
     if (dirty) {
+        const bool exists = texture;
         bind();
 
         std::lock_guard<std::mutex> lock(mtx);
-        glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, data);
+
+        if (!exists) {
+            glTexImage2D(
+                GL_TEXTURE_2D, // GLenum target
+                0, // GLint level
+                GL_ALPHA, // GLint internalformat
+                width, // GLsizei width
+                height, // GLsizei height
+                0, // GLint border
+                GL_ALPHA, // GLenum format
+                GL_UNSIGNED_BYTE, // GLenum type
+                data // const GLvoid * data
+            );
+        } else {
+            glTexSubImage2D(
+                GL_TEXTURE_2D, // GLenum target
+                0, // GLint level
+                0, // GLint xoffset
+                0, // GLint yoffset
+                width, // GLsizei width
+                height, // GLsizei height
+                GL_ALPHA, // GLenum format
+                GL_UNSIGNED_BYTE, // GLenum type
+                data // const GLvoid *pixels
+            );
+        }
         dirty = false;
 
 #if defined(DEBUG)
diff --git a/src/geometry/sprite_atlas.cpp b/src/geometry/sprite_atlas.cpp
index 3d7c1ecd0..730551dbe 100644
--- a/src/geometry/sprite_atlas.cpp
+++ b/src/geometry/sprite_atlas.cpp
@@ -215,7 +215,7 @@ void SpriteAtlas::bind(bool linear) {
 
 void SpriteAtlas::upload() {
     if (dirty) {
-        bool exists = texture;
+        const bool exists = texture;
         bind(filter); // Make sure we don't change the filter value.
 
         std::lock_guard<std::mutex> lock(mtx);
@@ -234,7 +234,8 @@ void SpriteAtlas::upload() {
                 data // const GLvoid * data
             );
         } else {
-            glTexSubImage2D(GL_TEXTURE_2D, // GLenum target
+            glTexSubImage2D(
+                GL_TEXTURE_2D, // GLenum target
                 0, // GLint level
                 0, // GLint xoffset
                 0, // GLint yoffset