diff --git a/fs_mgr/liblp/builder.cpp b/fs_mgr/liblp/builder.cpp
index cff44b7..9d710f9 100644
--- a/fs_mgr/liblp/builder.cpp
+++ b/fs_mgr/liblp/builder.cpp
@@ -200,6 +200,11 @@
     metadata_max_size = AlignTo(metadata_max_size, LP_SECTOR_SIZE);
 
     // Check that device properties are sane.
+    device_info_ = device_info;
+    if (device_info_.size % LP_SECTOR_SIZE != 0) {
+        LERROR << "Block device size must be a multiple of 512.";
+        return false;
+    }
     if (device_info_.alignment_offset % LP_SECTOR_SIZE != 0) {
         LERROR << "Alignment offset is not sector-aligned.";
         return false;
@@ -212,7 +217,6 @@
         LERROR << "Partition alignment offset is greater than its alignment.";
         return false;
     }
-    device_info_ = device_info;
 
     // We reserve a geometry block (4KB) plus space for each copy of the
     // maximum size of a metadata blob. Then, we double that space since
diff --git a/fs_mgr/liblp/builder_test.cpp b/fs_mgr/liblp/builder_test.cpp
index 08440a3..b610fd4 100644
--- a/fs_mgr/liblp/builder_test.cpp
+++ b/fs_mgr/liblp/builder_test.cpp
@@ -106,19 +106,9 @@
     static const uint32_t kMetadataSize = 1024;
     static const uint32_t kMetadataSlots = 2;
 
-    // If the disk size is not aligned to 512 bytes, make sure it still leaves
-    // space at the end for backup metadata, and that it doesn't overlap with
-    // the space for logical partitions.
     unique_ptr<MetadataBuilder> builder =
             MetadataBuilder::New(kDiskSize, kMetadataSize, kMetadataSlots);
-    unique_ptr<LpMetadata> exported = builder->Export();
-    ASSERT_NE(exported, nullptr);
-
-    static const size_t kMetadataSpace =
-            (kMetadataSize * kMetadataSlots) + LP_METADATA_GEOMETRY_SIZE;
-    uint64_t space_at_end =
-            kDiskSize - (exported->geometry.last_logical_sector + 1) * LP_SECTOR_SIZE;
-    EXPECT_GE(space_at_end, kMetadataSpace);
+    ASSERT_EQ(builder, nullptr);
 }
 
 TEST(liblp, MetadataAlignment) {
@@ -148,15 +138,10 @@
     EXPECT_EQ(exported->geometry.first_logical_sector, 1472);
     EXPECT_EQ(exported->geometry.last_logical_sector, 2035);
 
-    // Test only an alignment offset (which should simply bump up the first
-    // logical sector).
+    // Alignment offset without alignment doesn't mean anything.
     device_info.alignment = 0;
     builder = MetadataBuilder::New(device_info, 1024, 2);
-    ASSERT_NE(builder, nullptr);
-    exported = builder->Export();
-    ASSERT_NE(exported, nullptr);
-    EXPECT_EQ(exported->geometry.first_logical_sector, 1484);
-    EXPECT_EQ(exported->geometry.last_logical_sector, 2035);
+    ASSERT_EQ(builder, nullptr);
 
     // Test a small alignment with an alignment offset.
     device_info.alignment = 12 * 1024;
diff --git a/fs_mgr/liblp/include/liblp/metadata_format.h b/fs_mgr/liblp/include/liblp/metadata_format.h
index b69e138..e1323e1 100644
--- a/fs_mgr/liblp/include/liblp/metadata_format.h
+++ b/fs_mgr/liblp/include/liblp/metadata_format.h
@@ -86,7 +86,9 @@
     /*  8: SHA256 checksum of this struct, with this field set to 0. */
     uint8_t checksum[32];
 
-    /* 40: Maximum amount of space a single copy of the metadata can use. */
+    /* 40: Maximum amount of space a single copy of the metadata can use. This
+     * must be a multiple of LP_SECTOR_SIZE.
+     */
     uint32_t metadata_max_size;
 
     /* 44: Number of copies of the metadata to keep. For A/B devices, this
diff --git a/fs_mgr/liblp/reader.cpp b/fs_mgr/liblp/reader.cpp
index 985cf09..7fbf8e6 100644
--- a/fs_mgr/liblp/reader.cpp
+++ b/fs_mgr/liblp/reader.cpp
@@ -68,6 +68,10 @@
         LERROR << "Logical partition metadata has invalid slot count.";
         return false;
     }
+    if (geometry->metadata_max_size % LP_SECTOR_SIZE != 0) {
+        LERROR << "Metadata max size is not sector-aligned.";
+        return false;
+    }
 
     // Check that the metadata area and logical partition areas don't overlap.
     int64_t end_of_metadata =