diff --git a/src/opengl/qopengltextureglyphcache.cpp b/src/opengl/qopengltextureglyphcache.cpp
index 0bab710b..46bad551 100644
--- a/src/opengl/qopengltextureglyphcache.cpp
+++ b/src/opengl/qopengltextureglyphcache.cpp
@@ -108,14 +108,20 @@ void QOpenGLTextureGlyphCache::createTextureData(int width, int height)
         for (int i = 0; i < data.size(); ++i)
             data[i] = 0;
 #if !QT_CONFIG(opengles2)
         const GLint internalFormat = isCoreProfile() ? GL_R8 : GL_ALPHA;
         const GLenum format = isCoreProfile() ? GL_RED : GL_ALPHA;
 #else
-        const GLint internalFormat = GL_ALPHA;
-        const GLenum format = GL_ALPHA;
+        // qt6-base-fourier: OpenGL ES 3.x removed GL_ALPHA from
+        // glTexImage2D's valid internalFormat list (ES 3 spec
+        // section 3.8.3, table 3.13). Pick GL_R8 + matching format
+        // when the runtime context is ES 3 or newer; only legacy
+        // ES 2 contexts fall through to the historic GL_ALPHA path.
+        const bool useR8 = ctx->format().majorVersion() >= 3;
+        const GLint internalFormat = useR8 ? GL_R8 : GL_ALPHA;
+        const GLenum format = useR8 ? GL_RED : GL_ALPHA;
 #endif
         funcs->glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, &data[0]);
     }
 
     funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
     funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
@@ -210,13 +216,14 @@ static void load_glyph_image_to_texture(QOpenGLContext *ctx,
     } else {
         // The scanlines in image are 32-bit aligned, even for mono or 8-bit formats. This
         // is good because it matches the default of 4 bytes for GL_UNPACK_ALIGNMENT.
 #if !QT_CONFIG(opengles2)
         const GLenum format = isCoreProfile() ? GL_RED : GL_ALPHA;
 #else
-        const GLenum format = GL_ALPHA;
+        // qt6-base-fourier: ES 3 path — see createTextureData() above.
+        const GLenum format = ctx->format().majorVersion() >= 3 ? GL_RED : GL_ALPHA;
 #endif
         funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, tx, ty, imgWidth, imgHeight, format, GL_UNSIGNED_BYTE, img.constBits());
     }
 }
 
 static void load_glyph_image_region_to_texture(QOpenGLContext *ctx,