diff --git a/dynamic.c b/dynamic.c
index 729a2f45b5..e3cfb19f31 100644
--- a/dynamic.c
+++ b/dynamic.c
@@ -927,6 +927,32 @@ bool rarch_environment_cb(unsigned cmd, void *data)
          break;
       }
 
+      case RETRO_ENVIRONMENT_SET_GEOMETRY:
+      {
+         RARCH_LOG("Environ SET_GEOMETRY.\n");
+         const struct retro_game_geometry *in_geom = (const struct retro_game_geometry*)data;
+         struct retro_game_geometry *geom = &g_extern.system.av_info.geometry;
+
+         // Can potentially be called every frame, don't do anything unless required.
+         if (geom->base_width != in_geom->base_width ||
+               geom->base_height != in_geom->base_height ||
+               geom->aspect_ratio != in_geom->aspect_ratio)
+         {
+            geom->base_width   = in_geom->base_width;
+            geom->base_height  = in_geom->base_height;
+            geom->aspect_ratio = in_geom->aspect_ratio;
+            RARCH_LOG("SET_GEOMETRY: %ux%u, aspect: %.3f.\n",
+                  geom->base_width, geom->base_height, geom->aspect_ratio);
+
+            // Forces recomputation of aspect ratios if using core-dependent aspect ratios.
+            if (driver.video_poke && driver.video_poke->set_aspect_ratio && driver.video_data)
+               driver.video_poke->set_aspect_ratio(driver.video_data, g_settings.video.aspect_ratio_idx);
+            
+            // TODO: Figure out what to do, if anything, with recording.
+         }
+         break;
+      }
+
       // Private extensions for internal use, not part of libretro API.
       case RETRO_ENVIRONMENT_SET_LIBRETRO_PATH:
          RARCH_LOG("Environ (Private) SET_LIBRETRO_PATH.\n");
diff --git a/libretro-test/libretro-test.c b/libretro-test/libretro-test.c
index 040374884a..d2db96d1a7 100644
--- a/libretro-test/libretro-test.c
+++ b/libretro-test/libretro-test.c
@@ -310,6 +310,7 @@ static void check_variables(void)
    float last_rate = last_sample_rate;
    struct retro_system_av_info info;
    retro_get_system_av_info(&info);
+
    if ((last != last_aspect && last != 0.0f) || (last_rate != last_sample_rate && last_rate != 0.0f))
    {
       // SET_SYSTEM_AV_INFO can only be called within retro_run().
@@ -317,8 +318,12 @@ static void check_variables(void)
       // on last and last_rate ensures this path is never hit that early.
       // last_aspect and last_sample_rate are not updated until retro_get_system_av_info(),
       // which must come after retro_load_game().
-      bool ret = environ_cb(RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO, &info);
-      logging.log(RETRO_LOG_INFO, "SET_SYSTEM_AV_INFO = %u.\n", ret);
+      bool ret;
+      if (last_rate != last_sample_rate && last_rate != 0.0f) // If audio rate changes, go through SET_SYSTEM_AV_INFO.
+         ret = environ_cb(RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO, &info);
+      else // If only aspect changed, take the simpler path.
+         ret = environ_cb(RETRO_ENVIRONMENT_SET_GEOMETRY, &info.geometry);
+      logging.log(RETRO_LOG_INFO, "SET_SYSTEM_AV_INFO/SET_GEOMETRY = %u.\n", ret);
    }
 }
 
diff --git a/libretro.h b/libretro.h
index 59a0e1df3c..d132fb101a 100755
--- a/libretro.h
+++ b/libretro.h
@@ -591,8 +591,8 @@ enum retro_mod
                                            // avoid setting the "worst case" in max_width/max_height.
                                            //
                                            // ***HIGHLY RECOMMENDED*** Do not call this callback every time resolution changes in an emulator core if it's
-                                           // expected to be a temporary change, for the reasons of possible driver reinit.
-                                           // This call is not a free pass for not trying to provide correct values in retro_get_system_av_info().
+                                           // expected to be a temporary change, for the reasons of possible driver reinitialization.
+                                           // This call is not a free pass for not trying to provide correct values in retro_get_system_av_info(). If you need to change things like aspect ratio or nominal width/height, use RETRO_ENVIRONMENT_SET_GEOMETRY, which is a softer variant of SET_SYSTEM_AV_INFO.
                                            //
                                            // If this returns false, the frontend does not acknowledge a changed av_info struct.
 #define RETRO_ENVIRONMENT_SET_PROC_ADDRESS_CALLBACK 33
@@ -645,6 +645,23 @@ enum retro_mod
                                            //
                                            // Can be called from retro_init and retro_load_game.
                                            //
+#define RETRO_ENVIRONMENT_SET_GEOMETRY 37
+                                           // const struct retro_game_geometry * --
+                                           // This environment call is similar to SET_SYSTEM_AV_INFO for changing video parameters,
+                                           // but provides a guarantee that drivers will not be reinitialized.
+                                           // This can only be called from within retro_run().
+                                           //
+                                           // The purpose of this call is to allow a core to alter nominal width/heights as well as aspect ratios on-the-fly,
+                                           // which can be useful for some emulators to change in run-time.
+                                           //
+                                           // max_width/max_height arguments are ignored and cannot be changed
+                                           // with this call as this could potentially require a reinitialization or a non-constant time operation.
+                                           // If max_width/max_height are to be changed, SET_SYSTEM_AV_INFO is required.
+                                           //
+                                           // A frontend must guarantee that this environment call completes in constant time.
+
+
+
 
 #define RETRO_MEMDESC_CONST     (1 << 0)   // The frontend will never change this memory area once retro_load_game has returned.
 #define RETRO_MEMDESC_BIGENDIAN (1 << 1)   // The memory area contains big endian data. Default is little endian.