diff --git a/protocol/payload_update.c b/protocol/payload_update.c
index f8a1d6b..c66fbc6 100644
--- a/protocol/payload_update.c
+++ b/protocol/payload_update.c
@@ -115,16 +115,16 @@ static libhoth_error payload_update_erase_chunk(
       &request, sizeof(request), NULL, 0, NULL);
 }
 
+static const size_t kBlockErase = 64 * 1024;
+static const size_t kSectorErase = 4 * 1024;
+
 libhoth_error libhoth_payload_update_erase(struct libhoth_device* const dev,
                                            const uint32_t offset,
                                            const uint32_t len) {
   struct libhoth_progress_stderr erase_progress;
   libhoth_progress_stderr_init(&erase_progress, "Erase staging side");
 
-  const size_t block_erase = 64 * 1024;
-  const size_t sector_erase = 4 * 1024;
-
-  if (len == 0 || (len % sector_erase) != 0) {
+  if (len == 0 || (len % kSectorErase) != 0) {
     fprintf(stderr,
             "error: erase length (0x%" PRIx32
             ") is zero or not sector-aligned.\n",
@@ -132,7 +132,7 @@ libhoth_error libhoth_payload_update_erase(struct libhoth_device* const dev,
     return LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
                                  LIBHOTH_ERR_IMAGE_NOT_SECTOR_ALIGNED);
   }
-  if ((offset % sector_erase) != 0) {
+  if ((offset % kSectorErase) != 0) {
     fprintf(stderr, "error: offset (0x%" PRIx32 ") is not sector-aligned.\n",
             offset);
     return LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
@@ -154,8 +154,8 @@ libhoth_error libhoth_payload_update_erase(struct libhoth_device* const dev,
     const uint32_t current_offset = offset + erased;
     const uint32_t remaining = len - erased;
     const bool send_block_erase =
-        (current_offset % block_erase == 0) && (remaining >= block_erase);
-    const uint32_t chunk_size = send_block_erase ? block_erase : sector_erase;
+        (current_offset % kBlockErase == 0) && (remaining >= kBlockErase);
+    const uint32_t chunk_size = send_block_erase ? kBlockErase : kSectorErase;
     const libhoth_error ret =
         payload_update_erase_chunk(dev, current_offset, chunk_size);
     if (ret != HOTH_SUCCESS) {
@@ -178,7 +178,21 @@ libhoth_error libhoth_payload_update(struct libhoth_device* dev, uint8_t* image,
   }
 
   if (!skip_erase) {
-    libhoth_error err = libhoth_payload_update_erase(dev, 0, size);
+    size_t erase_size = size;
+    if (binary_file && (erase_size % kSectorErase) != 0) {
+      const size_t pad = kSectorErase - (erase_size % kSectorErase);
+      if (erase_size > UINT32_MAX - pad) {
+        return LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
+                                     LIBHOTH_ERR_INVALID_PARAMETER);
+      }
+      erase_size += pad;
+    }
+    if (erase_size > UINT32_MAX) {
+      return LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
+                                   LIBHOTH_ERR_INVALID_PARAMETER);
+    }
+    libhoth_error err =
+        libhoth_payload_update_erase(dev, 0, (uint32_t)erase_size);
     if (err != HOTH_SUCCESS) {
       return err;
     }
diff --git a/protocol/payload_update_test.cc b/protocol/payload_update_test.cc
index 730740c..c59d37e 100644
--- a/protocol/payload_update_test.cc
+++ b/protocol/payload_update_test.cc
@@ -41,6 +41,8 @@ constexpr int kCmd =
 constexpr int64_t kMagic = 0x5F435344474D495F;
 constexpr int64_t kAlign = 1 << 16;
 constexpr int64_t kDummy = 0;
+constexpr size_t kBlockErase = 64 * 1024;
+constexpr size_t kSectorErase = 4 * 1024;
 
 MATCHER_P2(IsEraseRequest, offset, len, "") {
   const struct hoth_host_request* req =
@@ -461,6 +463,66 @@ TEST_F(LibHothTest, payload_update_test_with_binary_image) {
             HOTH_SUCCESS);
 }
 
+TEST_F(LibHothTest, payload_update_unaligned_binary_rounds_up_erase) {
+  constexpr size_t kUnalignedSize = kBlockErase + 100;
+  uint8_t buffer[kUnalignedSize];
+  std::memset(buffer, 0xFF, kUnalignedSize);
+  buffer[0] = 0xAA;
+
+  {
+    InSequence s;
+
+    // 64KB Block Erase for [0, 64KB)
+    EXPECT_CALL(mock_, send(_, IsEraseRequest(0, kBlockErase), _))
+        .WillOnce(Return(LIBHOTH_OK));
+    EXPECT_CALL(mock_, receive)
+        .WillOnce(DoAll(CopyResp(&kDummy, 0), Return(LIBHOTH_OK)));
+
+    // 4KB Sector Erase for [64KB, 68KB) rounded up from 64KB + 100B
+    EXPECT_CALL(mock_, send(_, IsEraseRequest(kBlockErase, kSectorErase), _))
+        .WillOnce(Return(LIBHOTH_OK));
+    EXPECT_CALL(mock_, receive)
+        .WillOnce(DoAll(CopyResp(&kDummy, 0), Return(LIBHOTH_OK)));
+
+    // Flash payload data
+    EXPECT_CALL(mock_, send(_, UsesCommand(kCmd), _))
+        .WillOnce(Return(LIBHOTH_OK));
+    EXPECT_CALL(mock_, receive)
+        .WillOnce(DoAll(CopyResp(&kDummy, 0), Return(LIBHOTH_OK)));
+  }
+
+  EXPECT_EQ(libhoth_payload_update(&hoth_dev_, buffer, kUnalignedSize,
+                                   /*skip_erase=*/false,
+                                   /*binary_file=*/true),
+            HOTH_SUCCESS);
+}
+
+TEST_F(LibHothTest, payload_update_unaligned_non_binary_fails) {
+  constexpr size_t kUnalignedSize = kSectorErase + 100;
+  uint8_t buffer[kUnalignedSize] = {0};
+
+  struct image_descriptor desc = {};
+  desc.descriptor_magic = TITAN_IMAGE_DESCRIPTOR_MAGIC;
+  desc.descriptor_area_size = sizeof(desc);
+  std::memcpy(buffer, &desc, sizeof(desc));
+
+  EXPECT_EQ(libhoth_payload_update(&hoth_dev_, buffer, kUnalignedSize,
+                                   /*skip_erase=*/false,
+                                   /*binary_file=*/false),
+            LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
+                                  LIBHOTH_ERR_IMAGE_NOT_SECTOR_ALIGNED));
+}
+
+TEST_F(LibHothTest, payload_update_unaligned_binary_erase_overflow_fails) {
+  uint8_t dummy = 0;
+  // Rounding 0xFFFFF001 up to the next 4 KiB boundary would overflow uint32_t.
+  EXPECT_EQ(libhoth_payload_update(&hoth_dev_, &dummy, 0xFFFFF001u,
+                                   /*skip_erase=*/false,
+                                   /*binary_file=*/true),
+            LIBHOTH_ERR_CONSTRUCT(HOTH_CTX_CMD_EXEC, HOTH_HOST_SPACE_LIBHOTH,
+                                  LIBHOTH_ERR_INVALID_PARAMETER));
+}
+
 TEST_F(LibHothTest, payload_update_erase_cmd_test) {
   constexpr size_t kBlockErase = 64 * 1024;
   constexpr size_t kSectorErase = 4 * 1024;