diff --git a/CHANGELOG.md b/CHANGELOG.md
index a63eb4a..78a2b32 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,8 @@ Changelog
 0.3.6 (not released yet)
 ------------------------
 Bug fixes:
-* Create directory entry with `VOLUME_ID` attribute when formatting if volume label was set in `FormatVolumeOptions`.
+* Create directory entry with `VOLUME_ID` attribute when formatting if volume label was set in `FormatVolumeOptions`
+* Fix `format_volume` function panicking in debug build for FAT12 volumes with size below 1 MB
 
 0.3.5 (2021-01-23)
 ------------------------
diff --git a/src/boot_sector.rs b/src/boot_sector.rs
index 4faf13a..0fd80da 100644
--- a/src/boot_sector.rs
+++ b/src/boot_sector.rs
@@ -449,8 +449,12 @@ fn determine_bytes_per_cluster(total_bytes: u64, bytes_per_sector: u16, fat_type
         },
     };
     const MAX_CLUSTER_SIZE: u32 = 32 * KB as u32;
-    debug_assert!(bytes_per_cluster.is_power_of_two());
-    cmp::min(cmp::max(bytes_per_cluster, bytes_per_sector as u32), MAX_CLUSTER_SIZE)
+    let bytes_per_cluster_clamped = cmp::min(
+        cmp::max(bytes_per_cluster, u32::from(bytes_per_sector)),
+        MAX_CLUSTER_SIZE,
+    );
+    debug_assert!(bytes_per_cluster_clamped.is_power_of_two());
+    bytes_per_cluster_clamped
 }
 
 fn determine_sectors_per_fat(
@@ -727,6 +731,7 @@ mod tests {
 
     #[test]
     fn test_determine_bytes_per_cluster_fat12() {
+        assert_eq!(determine_bytes_per_cluster(128 * KB, 512, Some(FatType::Fat12)), 512);
         assert_eq!(determine_bytes_per_cluster(1 * MB + 0, 512, Some(FatType::Fat12)), 512);
         assert_eq!(determine_bytes_per_cluster(1 * MB + 1, 512, Some(FatType::Fat12)), 1024);
         assert_eq!(determine_bytes_per_cluster(1 * MB, 4096, Some(FatType::Fat12)), 4096);