diff --git a/libsdhcdrivers/src/mmc.c b/libsdhcdrivers/src/mmc.c
index 22d518d..ce09f7a 100644
--- a/libsdhcdrivers/src/mmc.c
+++ b/libsdhcdrivers/src/mmc.c
@@ -256,12 +256,17 @@
     cmd.rsp_type = MMC_RSP_TYPE_R1b;
     host_send_command(card, &cmd, NULL, NULL);
 
-    /* Set Bus width */
+    /**
+     * The default bus width of the card after power up or GO_IDLE (CMD0) is
+     * 1 bit. As the HostController is initialzed to 4-bit bus width,
+     * the card also needs to switch to 4-bit mode.
+     */
     cmd.index = MMC_APP_CMD;
     cmd.arg = card->raw_rca << 16;
     cmd.rsp_type = MMC_RSP_TYPE_R1;
     host_send_command(card, &cmd, NULL, NULL);
     cmd.index = SD_SET_BUS_WIDTH;
+    cmd.arg = MMC_MODE_4BIT;
     host_send_command(card, &cmd, NULL, NULL);
 
     /* Set read/write block length for byte addressed standard capacity cards */
diff --git a/libsdhcdrivers/src/mmc.h b/libsdhcdrivers/src/mmc.h
index 602172c..ea53a81 100644
--- a/libsdhcdrivers/src/mmc.h
+++ b/libsdhcdrivers/src/mmc.h
@@ -75,6 +75,10 @@
 #define MMC_VDD_30_31             (1 << 18)
 #define MMC_VDD_29_30             (1 << 17)
 
+/* Bus width */
+#define MMC_MODE_8BIT       0x04
+#define MMC_MODE_4BIT       0x02
+
 
 enum mmc_rsp_type {
     MMC_RSP_TYPE_NONE = 0,
diff --git a/libsdhcdrivers/src/sdhc.c b/libsdhcdrivers/src/sdhc.c
index 7710ef7..08f8d87 100644
--- a/libsdhcdrivers/src/sdhc.c
+++ b/libsdhcdrivers/src/sdhc.c
@@ -625,6 +625,11 @@
 
     /* TODO: Select Voltage Level */
 
+    /* Set bus width */
+    val = readl(host->base + PROT_CTRL);
+    val |= MMC_MODE_4BIT;
+    writel(val, host->base + PROT_CTRL);
+
     /* Wait until the Command and Data Lines are ready. */
     while ((readl(host->base + PRES_STATE) & PRES_STATE_CDIHB) ||
            (readl(host->base + PRES_STATE) & PRES_STATE_CIHB));