diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1fe2e6..0c53d22 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,6 +21,7 @@ if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Release)
 endif()
 
+set(CMAKE_C_VISIBILITY_PRESET hidden)
 set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
diff --git a/include/olm/megolm.h b/include/olm/megolm.h
index e4e5d0b..338ab21 100644
--- a/include/olm/megolm.h
+++ b/include/olm/megolm.h
@@ -23,6 +23,10 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+// Note: exports in this file are only for unit tests.  Nobody else should be
+// using this externally
+#include "olm/olm_export.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -59,25 +63,25 @@ extern const struct _olm_cipher *megolm_cipher;
  * initialize the megolm ratchet. random_data should be at least
  * MEGOLM_RATCHET_LENGTH bytes of randomness.
  */
-void megolm_init(Megolm *megolm, uint8_t const *random_data, uint32_t counter);
+OLM_EXPORT void megolm_init(Megolm *megolm, uint8_t const *random_data, uint32_t counter);
 
 /** Returns the number of bytes needed to store a megolm */
-size_t megolm_pickle_length(const Megolm *megolm);
+OLM_EXPORT size_t megolm_pickle_length(const Megolm *megolm);
 
 /**
  * Pickle the megolm. Returns a pointer to the next free space in the buffer.
  */
-uint8_t * megolm_pickle(const Megolm *megolm, uint8_t *pos);
+OLM_EXPORT uint8_t * megolm_pickle(const Megolm *megolm, uint8_t *pos);
 
 /**
  * Unpickle the megolm. Returns a pointer to the next item in the buffer.
  */
-const uint8_t * megolm_unpickle(Megolm *megolm, const uint8_t *pos,
+OLM_EXPORT const uint8_t * megolm_unpickle(Megolm *megolm, const uint8_t *pos,
                                 const uint8_t *end);
 
 
 /** advance the ratchet by one step */
-void megolm_advance(Megolm *megolm);
+OLM_EXPORT void megolm_advance(Megolm *megolm);
 
 /**
  * get the key data in the ratchet. The returned data is
@@ -86,7 +90,7 @@ void megolm_advance(Megolm *megolm);
 #define megolm_get_data(megolm) ((const uint8_t *)((megolm)->data))
 
 /** advance the ratchet to a given count */
-void megolm_advance_to(Megolm *megolm, uint32_t advance_to);
+OLM_EXPORT void megolm_advance_to(Megolm *megolm, uint32_t advance_to);
 
 #ifdef __cplusplus
 } // extern "C"
diff --git a/include/olm/pickle_encoding.h b/include/olm/pickle_encoding.h
index 03611df..ec2a2d6 100644
--- a/include/olm/pickle_encoding.h
+++ b/include/olm/pickle_encoding.h
@@ -23,6 +23,10 @@
 
 #include "olm/error.h"
 
+// Note: exports in this file are only for unit tests.  Nobody else should be
+// using this externally
+#include "olm/olm_export.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -31,7 +35,7 @@ extern "C" {
 /**
  * Get the number of bytes needed to encode a pickle of the length given
  */
-size_t _olm_enc_output_length(size_t raw_length);
+OLM_EXPORT size_t _olm_enc_output_length(size_t raw_length);
 
 /**
  * Get the point in the output buffer that the raw pickle should be written to.
@@ -41,7 +45,7 @@ size_t _olm_enc_output_length(size_t raw_length);
  * base-64 encoding would otherwise overwrite the end of the input before it
  * was encoded.)
  */
- uint8_t *_olm_enc_output_pos(uint8_t * output, size_t raw_length);
+OLM_EXPORT uint8_t *_olm_enc_output_pos(uint8_t * output, size_t raw_length);
 
 /**
  * Encrypt and encode the given pickle in-situ.
@@ -51,7 +55,7 @@ size_t _olm_enc_output_length(size_t raw_length);
  *
  * Returns the number of bytes in the encoded pickle.
  */
-size_t _olm_enc_output(
+OLM_EXPORT size_t _olm_enc_output(
     uint8_t const * key, size_t key_length,
     uint8_t *pickle, size_t raw_length
 );
@@ -62,7 +66,7 @@ size_t _olm_enc_output(
  * Returns the number of bytes in the decoded pickle, or olm_error() on error,
  * in which case *last_error will be updated, if last_error is non-NULL.
  */
-size_t _olm_enc_input(
+OLM_EXPORT size_t _olm_enc_input(
     uint8_t const * key, size_t key_length,
     uint8_t * input, size_t b64_length,
     enum OlmErrorCode * last_error