diff --git a/fastfield_codecs/src/linearinterpol.rs b/fastfield_codecs/src/linearinterpol.rs
index 1bf7c8b9c..b5a6fa25d 100644
--- a/fastfield_codecs/src/linearinterpol.rs
+++ b/fastfield_codecs/src/linearinterpol.rs
@@ -151,9 +151,13 @@ impl LinearInterpolFastFieldSerializer {
         Ok(())
     }
 }
+
 fn get_slope(first_val: u64, last_val: u64, num_vals: u64) -> f32 {
+    if num_vals <= 1 {
+        return 0.0;
+    }
     //  We calculate the slope with f64 high precision and use the result in lower precision f32
-    //  This is done in order to handle estimation for very large values like i64::MAX
+    //  This is done in order to handle estimations for very large values like i64::MAX
     ((last_val as f64 - first_val as f64) / (num_vals as u64 - 1) as f64) as f32
 }
 
diff --git a/src/fastfield/reader.rs b/src/fastfield/reader.rs
index 8cb7ec089..ad408af1f 100644
--- a/src/fastfield/reader.rs
+++ b/src/fastfield/reader.rs
@@ -142,7 +142,8 @@ impl<Item: FastValue, C: CodecReader> FastFieldReaderCodecWrapper<Item, C> {
     /// Opens a fast field given a file.
     pub fn open(file: FileSlice) -> crate::Result<Self> {
         let mut bytes = file.read_bytes()?;
-        let _id = u8::deserialize(&mut bytes)?;
+        let id = u8::deserialize(&mut bytes)?;
+        assert_eq!(BitpackedFastFieldSerializer::<Vec<u8>>::ID, id);
         Self::open_from_bytes(bytes)
     }
     /// Opens a fast field given the bytes.
diff --git a/src/fastfield/serializer/mod.rs b/src/fastfield/serializer/mod.rs
index 8a48199a6..954823a13 100644
--- a/src/fastfield/serializer/mod.rs
+++ b/src/fastfield/serializer/mod.rs
@@ -44,7 +44,7 @@ impl CompositeFastFieldSerializer {
         Ok(CompositeFastFieldSerializer { composite_write })
     }
 
-    /// Serialize data into a new u64 fast field. The compression will be detected automatically.
+    /// Serialize data into a new u64 fast field. The best compression codec will be chosen automatically.
     pub fn create_auto_detect_u64_fast_field(
         &mut self,
         field: Field,
@@ -76,8 +76,23 @@ impl CompositeFastFieldSerializer {
             );
             estimations.push((ratio, name, id));
         }
+        if let Some(broken_estimation) = estimations
+            .iter()
+            .find(|estimation| estimation.0 == f32::NAN)
+        {
+            warn!(
+                "broken estimation for fast field codec {}",
+                broken_estimation.1
+            );
+        }
+        // removing nan values for codecs with broken calculations, and max values which disables codecs
+        estimations.retain(|estimation| !estimation.0.is_nan() && estimation.0 != f32::MAX);
         estimations.sort_by(|a, b| a.0.partial_cmp(&b.0).unwrap());
         let (_ratio, name, id) = estimations[0];
+        debug!(
+            "choosing fast field codec {} for field_id {:?}",
+            name, field
+        ); // todo print acutal field name
         id.serialize(field_write)?;
         match name {
             BitpackedFastFieldSerializer::<Vec<u8>>::NAME => {