diff --git a/src/shared/dissect-image.c b/src/shared/dissect-image.c
index 9944d6c855..a392f2a949 100644
--- a/src/shared/dissect-image.c
+++ b/src/shared/dissect-image.c
@@ -1309,7 +1309,7 @@ static int dissect_image(
                 start = sym_blkid_partition_get_start(pp);
                 if (start < 0)
                         return errno_or_else(EIO);
-                if ((uint64_t) start >= UINT64_MAX/512)
+                if ((uint64_t) start > INT64_MAX / 512)
                         return log_debug_errno(SYNTHETIC_ERRNO(EOVERFLOW),
                                                "Partition start LBA too large to convert to a byte offset, refusing.");
 
@@ -1317,10 +1317,15 @@ static int dissect_image(
                 size = sym_blkid_partition_get_size(pp);
                 if (size < 0)
                         return errno_or_else(EIO);
-                if ((uint64_t) size >= UINT64_MAX/512)
+                if ((uint64_t) size > INT64_MAX / 512)
                         return log_debug_errno(SYNTHETIC_ERRNO(EOVERFLOW),
                                                "Partition size in LBA too large to convert to a byte offset, refusing.");
 
+                /* Ensure the partition's exclusive end LBA can be converted to a byte offset. */
+                if ((uint64_t) start + (uint64_t) size > INT64_MAX / 512)
+                        return log_debug_errno(SYNTHETIC_ERRNO(EOVERFLOW),
+                                               "Partition end LBA too large to convert to a byte offset, refusing.");
+
                 /* While probing we need the non-diskseq device node name to access the thing, hence mask off
                  * DISSECT_IMAGE_DISKSEQ_DEVNODE. */
                 r = make_partition_devname(devname, diskseq, nr, flags & ~DISSECT_IMAGE_DISKSEQ_DEVNODE, &node);