diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,14 @@
 # Changelog for data-sketches-core
 
+## 0.2.0.1
+
+### Bug fixes
+
+- **Missing `include-dirs` for C headers**: `cbits/req.c` includes `req.h` but the
+  cabal file had no `include-dirs` entry pointing at `cbits/`, causing a build failure
+  (`fatal error: req.h: No such file or directory`). Added `include-dirs: cbits` and
+  listed header files in `extra-source-files` so they're included in sdist tarballs.
+
 ## 0.2.0.0
 
 ### New sketch families
diff --git a/cbits/kll.h b/cbits/kll.h
new file mode 100644
--- /dev/null
+++ b/cbits/kll.h
@@ -0,0 +1,20 @@
+#ifndef KLL_H
+#define KLL_H
+
+#include <stdint.h>
+
+typedef struct kll_sketch kll_sketch_t;
+
+kll_sketch_t *kll_new(uint32_t k, uint64_t seed);
+void kll_free(kll_sketch_t *sk);
+void kll_insert(kll_sketch_t *sk, double val);
+uint64_t kll_count(const kll_sketch_t *sk);
+double kll_min(const kll_sketch_t *sk);
+double kll_max(const kll_sketch_t *sk);
+int kll_is_empty(const kll_sketch_t *sk);
+int kll_retained(const kll_sketch_t *sk);
+double kll_rank(const kll_sketch_t *sk, double value);
+double kll_quantile(const kll_sketch_t *sk, double norm_rank);
+void kll_merge(kll_sketch_t *dst, const kll_sketch_t *src);
+
+#endif
diff --git a/cbits/req.h b/cbits/req.h
new file mode 100644
--- /dev/null
+++ b/cbits/req.h
@@ -0,0 +1,30 @@
+#ifndef REQ_H
+#define REQ_H
+
+#include <stdint.h>
+
+typedef struct req_sketch req_sketch_t;
+
+req_sketch_t *req_new(uint32_t k, int rank_accuracy, uint64_t seed);
+void          req_free(req_sketch_t *sk);
+
+void     req_insert(req_sketch_t *sk, double val);
+void     req_merge(req_sketch_t *dst, const req_sketch_t *src);
+
+uint64_t req_count(const req_sketch_t *sk);
+int      req_is_empty(const req_sketch_t *sk);
+double   req_min(const req_sketch_t *sk);
+double   req_max(const req_sketch_t *sk);
+double   req_sum(const req_sketch_t *sk);
+int      req_retained(const req_sketch_t *sk);
+uint32_t req_k(const req_sketch_t *sk);
+int      req_rank_accuracy(const req_sketch_t *sk);
+int      req_num_levels(const req_sketch_t *sk);
+int      req_criterion(const req_sketch_t *sk);
+void     req_set_criterion(req_sketch_t *sk, int crit);
+
+uint64_t req_count_with_criterion(req_sketch_t *sk, double value);
+double   req_rank(req_sketch_t *sk, double value);
+double   req_quantile(req_sketch_t *sk, double norm_rank);
+
+#endif
diff --git a/data-sketches-core.cabal b/data-sketches-core.cabal
--- a/data-sketches-core.cabal
+++ b/data-sketches-core.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           data-sketches-core
-version:        0.2.0.0
+version:        0.2.0.1
 description:    Please see the README on GitHub at <https://github.com/iand675/datasketches-haskell#readme>
 homepage:       https://github.com/iand675/datasketches-haskell#readme
 bug-reports:    https://github.com/iand675/datasketches-haskell/issues
@@ -18,6 +18,8 @@
 extra-source-files:
     README.md
     ChangeLog.md
+    cbits/kll.h
+    cbits/req.h
 
 source-repository head
   type: git
@@ -52,6 +54,8 @@
       StandaloneDeriving
       TypeFamilies
       TypeOperators
+  include-dirs:
+      cbits
   cc-options: -O2
   c-sources:
       cbits/sketches.c