diff --git a/persistent-data/space-maps/disk.cc b/persistent-data/space-maps/disk.cc
index 614a38d..6e6fc71 100644
--- a/persistent-data/space-maps/disk.cc
+++ b/persistent-data/space-maps/disk.cc
@@ -43,11 +43,19 @@ namespace {
 			bitmap_header const *data = reinterpret_cast<bitmap_header const *>(raw);
 			crc32c sum(BITMAP_CSUM_XOR);
 			sum.append(&data->not_used, MD_BLOCK_SIZE - sizeof(uint32_t));
-			if (sum.get_sum() != to_cpu<uint32_t>(data->csum))
-				throw checksum_error("bad checksum in space map bitmap");
+			if (sum.get_sum() != to_cpu<uint32_t>(data->csum)) {
+				std::ostringstream out;
+				out << "bad checksum in space map bitmap (block "
+				    << location << ")";
+				throw checksum_error(out.str());
+			}
 
-			if (to_cpu<uint64_t>(data->blocknr) != location)
-				throw checksum_error("bad block nr in space map bitmap");
+			if (to_cpu<uint64_t>(data->blocknr) != location) {
+				std::ostringstream out;
+				out << "bad block nr in space map bitmap (block "
+				    << location << ")";
+				throw checksum_error(out.str());
+			}
 		}
 
 		virtual bool check_raw(void const *raw) const {
@@ -77,11 +85,19 @@ namespace {
 			metadata_index const *mi = reinterpret_cast<metadata_index const *>(raw);
 			crc32c sum(INDEX_CSUM_XOR);
 			sum.append(&mi->padding_, MD_BLOCK_SIZE - sizeof(uint32_t));
-			if (sum.get_sum() != to_cpu<uint32_t>(mi->csum_))
-				throw checksum_error("bad checksum in metadata index block");
+			if (sum.get_sum() != to_cpu<uint32_t>(mi->csum_)) {
+				std::ostringstream out;
+				out << "bad checksum in metadata index block (block "
+				    << location << ")";
+				throw checksum_error(out.str());
+			}
 
-			if (to_cpu<uint64_t>(mi->blocknr_) != location)
-				throw checksum_error("bad block nr in metadata index block");
+			if (to_cpu<uint64_t>(mi->blocknr_) != location) {
+				std::ostringstream out;
+				out << "bad block nr in metadata index block (block "
+				    << location << ")";
+				throw checksum_error(out.str());
+			}
 		}
 
 		virtual bool check_raw(void const *raw) const {