diff --git a/libraries/SD_MMC/examples/SDMMC_Test/SDMMC_Test.ino b/libraries/SD_MMC/examples/SDMMC_Test/SDMMC_Test.ino
index e03f5ceb25e..ffa8160be77 100644
--- a/libraries/SD_MMC/examples/SDMMC_Test/SDMMC_Test.ino
+++ b/libraries/SD_MMC/examples/SDMMC_Test/SDMMC_Test.ino
@@ -211,6 +211,25 @@ void testFileIO(fs::FS &fs, const char *path) {
   file.close();
 }
 
+void testRawIO(uint32_t sectors, uint8_t sequential) {
+  uint32_t readSect = 0;
+  uint32_t startTime = millis();
+  uint8_t* buf = (uint8_t*)heap_caps_malloc(SD_MMC.sectorSize(), MALLOC_CAP_DMA);
+  for (uint32_t x=0; x<sectors; x++) {
+    if (! SD_MMC.readRAW(buf, readSect)) {
+      log_e("Unable to read sector %lu\n", readSect);
+      free(buf);
+      return;
+    }
+    readSect = sequential ? readSect + 1 : random(SD_MMC.numSectors()-1);
+  }
+  uint32_t passed = millis() - startTime;
+  uint32_t rate = sectors * SD_MMC.sectorSize() / passed;
+  Serial.printf("%lu %s sectors read in %lu msec (%luKB/s)\n", 
+                 sectors, sequential ? "sequential" : "random", passed, rate);
+  free(buf);
+}
+
 void setup() {
   Serial.begin(115200);
   /*
@@ -262,6 +281,7 @@ void setup() {
   renameFile(SD_MMC, "/hello.txt", "/foo.txt");
   readFile(SD_MMC, "/foo.txt");
   testFileIO(SD_MMC, "/test.txt");
+  testRawIO(2000, 1);
   Serial.printf("Total space: %lluMB\n", SD_MMC.totalBytes() / (1024 * 1024));
   Serial.printf("Used space: %lluMB\n", SD_MMC.usedBytes() / (1024 * 1024));
 }
diff --git a/libraries/SD_MMC/src/SD_MMC.cpp b/libraries/SD_MMC/src/SD_MMC.cpp
index 12ab2b565eb..5d15c12d7f4 100644
--- a/libraries/SD_MMC/src/SD_MMC.cpp
+++ b/libraries/SD_MMC/src/SD_MMC.cpp
@@ -246,6 +246,15 @@ bool SDMMCFS::begin(const char *mountpoint, bool mode1bit, bool format_if_mount_
     .width = 4,
     .flags = 0,
   };
+#ifdef SOC_SDMMC_UHS_I_SUPPORTED
+  if (sdmmc_frequency == SDMMC_FREQ_DDR50) {
+    host.flags |= SDMMC_HOST_FLAG_DDR;
+    slot_config.flags = SDMMC_SLOT_FLAG_UHS1;
+  }
+  if (sdmmc_frequency == SDMMC_FREQ_SDR50) {
+    slot_config.flags = SDMMC_SLOT_FLAG_UHS1;
+  }
+#endif
 #else
   host.slot = SDMMC_HOST_SLOT_1;
 #endif
diff --git a/libraries/SD_MMC/src/SD_MMC.h b/libraries/SD_MMC/src/SD_MMC.h
index 7192d466b89..e20c6ccfaa9 100644
--- a/libraries/SD_MMC/src/SD_MMC.h
+++ b/libraries/SD_MMC/src/SD_MMC.h
@@ -30,8 +30,12 @@
 // you can define BOARD_MAX_SDMMC_FREQ with lower value (Ex. SDMMC_FREQ_DEFAULT)
 // in pins_arduino.h for your board variant.
 #ifndef BOARD_MAX_SDMMC_FREQ
+#ifdef SOC_SDMMC_UHS_I_SUPPORTED
+#define BOARD_MAX_SDMMC_FREQ SDMMC_FREQ_SDR50
+#else
 #define BOARD_MAX_SDMMC_FREQ SDMMC_FREQ_HIGHSPEED
 #endif
+#endif
 
 namespace fs {