diff --git a/build.py b/build.py
index 1836662..d5dd724 100644
--- a/build.py
+++ b/build.py
@@ -58,7 +58,7 @@
 
 cdef = [
     "typedef struct { ...; } bam_fset;"
-    "bam_fset* create_bam_fset(char* fname);"
+    "bam_fset* create_bam_fset(char* fname, char* fasta_path);"
     "void destroy_bam_fset(bam_fset* fset);"
 ]
 for header in ('clair3_pileup.h', 'clair3_full_alignment.h'):
diff --git a/preprocess/CreateTensorPileupFromCffi.py b/preprocess/CreateTensorPileupFromCffi.py
index e609c23..fde6260 100644
--- a/preprocess/CreateTensorPileupFromCffi.py
+++ b/preprocess/CreateTensorPileupFromCffi.py
@@ -47,7 +47,7 @@ def pileup_counts_clair3(
     """
     lib = libclair3.lib
     featlenclair3 = lib.featlenclair3
-    bam = BAMHandler(bam)
+    bam = BAMHandler(bam, fasta)
 
     def _process_region(reg):
         # ctg start is 1-based, medaka.common.Region object is 0-based
@@ -55,7 +55,7 @@ def _process_region(reg):
         if isinstance(bam, BAMHandler):
             bam_handle = bam
         else:
-            bam_handle = BAMHandler(bam)
+            bam_handle = BAMHandler(bam, fasta)
         with bam_handle.borrow() as fh:
             counts = lib.calculate_clair3_pileup(
                 region_str.encode(), fh, fasta.encode(), min_depth, min_snp_af, min_indel_af, min_mq, max_indel_length, call_snp_only, max_depth, gvcf)
@@ -88,7 +88,7 @@ def _process_region(reg):
 class BAMHandler(object):
     """Opening of BAM file handles and indices."""
 
-    def __init__(self, bam, size=16):
+    def __init__(self, bam, fasta, size=16):
         """Initialise a pool of HTSlib filehandles."""
         # note: the default size here is set to match the default
         #       `bam_workers` of prediction.DataLoader and `workers`
@@ -100,7 +100,7 @@ def __init__(self, bam, size=16):
         lib, ffi = libclair3.lib, libclair3.ffi
         for _ in range(size):
             fset = ffi.gc(
-                lib.create_bam_fset(self.bam.encode()),
+                lib.create_bam_fset(self.bam.encode(), fasta.encode()),
                 self._destroy_fset)
             self._pool.put(fset)
 
diff --git a/src/clair3_full_alignment.c b/src/clair3_full_alignment.c
index 7a59b01..962bee1 100644
--- a/src/clair3_full_alignment.c
+++ b/src/clair3_full_alignment.c
@@ -404,6 +404,7 @@ size_t min_mq, size_t min_bq, size_t matrix_depth, size_t max_indel_length)
     bam_hdr_t *header;
 
     hts_file = sam_open(bam_path, "r");
+    hts_set_opt(hts_file, CRAM_OPT_REFERENCE, fasta_path);
     idx = sam_index_load(hts_file, bam_path);
     header = sam_hdr_read(hts_file);
     const int tid = bam_name2id(header, chr);
diff --git a/src/medaka_bamiter.c b/src/medaka_bamiter.c
index c01e874..d6d4576 100644
--- a/src/medaka_bamiter.c
+++ b/src/medaka_bamiter.c
@@ -49,9 +49,10 @@ int read_bam(void *data, bam1_t *b) {
 
 
 // Initialise BAM file, index and header structures
-bam_fset* create_bam_fset(const char* fname) {
+bam_fset* create_bam_fset(const char* fname, const char* fasta_path) {
     bam_fset* fset = xalloc(1, sizeof(bam_fset), "bam fileset");
     fset->fp = hts_open(fname, "rb");
+    hts_set_opt(fset->fp, CRAM_OPT_REFERENCE, fasta_path);
     fset->idx = sam_index_load(fset->fp, fname);
     fset->hdr = sam_hdr_read(fset->fp);
     if (fset->hdr == 0 || fset->idx == 0 || fset->fp == 0) {
diff --git a/src/medaka_bamiter.h b/src/medaka_bamiter.h
index 100c632..3ea1100 100644
--- a/src/medaka_bamiter.h
+++ b/src/medaka_bamiter.h
@@ -25,7 +25,7 @@ typedef struct {
 
 
 // Initialise BAM file, index and header structures
-bam_fset* create_bam_fset(const char* fname);
+bam_fset* create_bam_fset(const char* fname, const char* fasta_path);
 
 // Destory BAM file, index and header structures
 void destroy_bam_fset(bam_fset* fset);