diff --git a/Cargo.toml b/Cargo.toml
index 7c64ecbc4..87107078f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,11 @@ readme = "README.md"
 keywords = ["search", "information", "retrieval"]
 edition = "2018"
 
+
+[[bin]]
+name = "debug_position"
+path = "src/debug_position.rs"
+
 [dependencies]
 base64 = "0.13"
 byteorder = "1.4.3"
diff --git a/src/debug_position.rs b/src/debug_position.rs
new file mode 100644
index 000000000..ca4dff58b
--- /dev/null
+++ b/src/debug_position.rs
@@ -0,0 +1,53 @@
+use std::panic;
+
+use tantivy;
+use tantivy::DocSet;
+use tantivy::Postings;
+use tantivy::Searcher;
+use tantivy::TERMINATED;
+use tantivy::schema::Field;
+use tantivy::schema::IndexRecordOption;
+
+fn test_field(searcher: &Searcher, field: Field) -> tantivy::Result<()> {
+    for segment_reader in searcher.segment_readers() {
+        println!("\n\n====\nsegment {:?}", segment_reader.segment_id());
+        println!("maxdoc {} del {} ", segment_reader.max_doc(), segment_reader.num_deleted_docs());
+        let inv_idx = segment_reader.inverted_index(field)?;
+        let termdict = inv_idx.terms();
+        println!("num terms {}", termdict.num_terms());
+        let mut terms = termdict.stream()?;
+        while terms.advance() {
+            let term_info = terms.value();
+            let mut postings = inv_idx.read_postings_from_terminfo(term_info, tantivy::schema::IndexRecordOption::WithFreqsAndPositions)?;
+            let mut seen_doc = 0;
+            while postings.doc() != TERMINATED {
+                let mut postings_clone= postings.clone();
+                // println!("termord {} seen_doc {} termpositions {:?} docfreq {}", terms.term_ord(), seen_doc, term_info.positions_range, term_info.doc_freq);
+                let mut positions = Vec::new();
+                postings_clone.positions(&mut positions);
+                seen_doc += 1;
+                postings.advance();
+            }
+        }
+    }
+    Ok(())
+}
+
+fn main() -> tantivy::Result<()> {
+    let index = tantivy::Index::open_in_dir(".")?;
+    let reader = index.reader()?;
+    let searcher = reader.searcher();
+    let schema = index.schema();
+    for (field, field_entry) in schema.fields() {
+        let field_type = field_entry.field_type();
+        let has_position = field_type.get_index_record_option()
+            .map(|opt| opt == IndexRecordOption::WithFreqsAndPositions)
+            .unwrap_or(false);
+        if !has_position {
+            continue;
+        }
+        test_field(&*searcher, field)?;
+    }
+
+    Ok(())
+}
diff --git a/src/directory/file_slice.rs b/src/directory/file_slice.rs
index bcd85a2f7..8c9f3d5bf 100644
--- a/src/directory/file_slice.rs
+++ b/src/directory/file_slice.rs
@@ -4,11 +4,12 @@ use crate::common::HasLen;
 use crate::directory::OwnedBytes;
 use std::fmt;
 use std::ops::Range;
+use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::sync::{Arc, Weak};
 use std::{io, ops::Deref};
 
-pub type ArcBytes = Arc<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
-pub type WeakArcBytes = Weak<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+pub type ArcBytes = Arc<dyn Deref<Target = [u8]> + Send + Sync + UnwindSafe + RefUnwindSafe + 'static>;
+pub type WeakArcBytes = Weak<dyn Deref<Target = [u8]> + Send + Sync + UnwindSafe + RefUnwindSafe + 'static>;
 
 /// Objects that represents files sections in tantivy.
 ///
@@ -40,7 +41,7 @@ impl<T: Deref<Target = [u8]>> HasLen for T {
 
 impl<B> From<B> for FileSlice
 where
-    B: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync,
+    B: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync + UnwindSafe + RefUnwindSafe,
 {
     fn from(bytes: B) -> FileSlice {
         FileSlice::new(Box::new(OwnedBytes::new(bytes)))
diff --git a/src/directory/mmap_directory.rs b/src/directory/mmap_directory.rs
index be0603271..29af3421e 100644
--- a/src/directory/mmap_directory.rs
+++ b/src/directory/mmap_directory.rs
@@ -20,6 +20,7 @@ use std::fs::OpenOptions;
 use std::fs::{self, File};
 use std::io::{self, Seek, SeekFrom};
 use std::io::{BufWriter, Read, Write};
+use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::path::{Path, PathBuf};
 use std::result;
 use std::sync::Arc;
@@ -314,7 +315,7 @@ impl TerminatingWrite for SafeFileWriter {
 }
 
 #[derive(Clone)]
-struct MmapArc(Arc<dyn Deref<Target = [u8]> + Send + Sync>);
+struct MmapArc(Arc<dyn Deref<Target = [u8]> + Send + Sync + RefUnwindSafe + UnwindSafe>);
 
 impl Deref for MmapArc {
     type Target = [u8];