diff --git a/crypto/CMakeLists.txt b/crypto/CMakeLists.txt
index 86fb4773a..35c22621a 100644
--- a/crypto/CMakeLists.txt
+++ b/crypto/CMakeLists.txt
@@ -1,6 +1,10 @@
 include_directories(. ../include)
 
-if (UNIX)
+if(APPLE)
+	set(PERLASM_STYLE macosx)
+	set(ASM_EXT S)
+	enable_language(ASM)
+else(UNIX)
 	set(PERLASM_STYLE elf)
 	set(ASM_EXT S)
 	enable_language(ASM)
diff --git a/crypto/base.h b/crypto/base.h
index 8a05899ef..a5ec844eb 100644
--- a/crypto/base.h
+++ b/crypto/base.h
@@ -75,6 +75,10 @@
 #error "Unknown target CPU"
 #endif
 
+#if defined(__APPLE__)
+#define OPENSSL_APPLE
+#endif
+
 #define OPENSSL_IS_BORINGSSL
 #define OPENSSL_VERSION_NUMBER 0x10002000
 
diff --git a/crypto/bn/bn_test.c b/crypto/bn/bn_test.c
index a49eadac9..440e1b65f 100644
--- a/crypto/bn/bn_test.c
+++ b/crypto/bn/bn_test.c
@@ -695,17 +695,6 @@ int rand_neg(void) {
 }
 
 static void print_word(BIO *bp, BN_ULONG w) {
-#ifdef OPENSSL_64_BIT
-  if (sizeof(w) > sizeof(unsigned long)) {
-    unsigned long h = (unsigned long)(w >> 32), l = (unsigned long)(w);
-
-    if (h)
-      BIO_printf(bp, "%lX%08lX", h, l);
-    else
-      BIO_printf(bp, "%lX", l);
-    return;
-  }
-#endif
   BIO_printf(bp, BN_HEX_FMT1, w);
 }
 
diff --git a/crypto/bn/internal.h b/crypto/bn/internal.h
index 3d6d75dba..afc92322c 100644
--- a/crypto/bn/internal.h
+++ b/crypto/bn/internal.h
@@ -125,6 +125,8 @@
 
 #include <openssl/base.h>
 
+#include <inttypes.h>
+
 #if defined(__cplusplus)
 extern "C" {
 #endif
@@ -156,11 +158,10 @@ void bn_correct_top(BIGNUM *bn);
 #define BN_MASK2h1	(0xffffffff80000000L)
 #define BN_TBIT		(0x8000000000000000L)
 #define BN_DEC_CONV	(10000000000000000000UL)
-#define BN_DEC_FMT1	"%lu"
-#define BN_DEC_FMT2	"%019lu"
+#define BN_DEC_FMT1	"%" PRIu64
+#define BN_DEC_FMT2	"%019" PRIu64
 #define BN_DEC_NUM	19
-#define BN_HEX_FMT1	"%lX"
-#define BN_HEX_FMT2	"%016lX"
+#define BN_HEX_FMT1	"%" PRIx64
 
 #elif defined(OPENSSL_32_BIT)
 
@@ -176,11 +177,10 @@ void bn_correct_top(BIGNUM *bn);
 #define BN_MASK2h	(0xffff0000L)
 #define BN_TBIT		(0x80000000L)
 #define BN_DEC_CONV	(1000000000L)
-#define BN_DEC_FMT1	"%u"
-#define BN_DEC_FMT2	"%09u"
+#define BN_DEC_FMT1	"%" PRIu32
+#define BN_DEC_FMT2	"%09" PRIu32
 #define BN_DEC_NUM	9
-#define BN_HEX_FMT1	"%X"
-#define BN_HEX_FMT2	"%08X"
+#define BN_HEX_FMT1	"%" PRIx32
 
 #else
 #error "Must define either OPENSSL_32_BIT or OPENSSL_64_BIT"
diff --git a/crypto/cpu-intel.c b/crypto/cpu-intel.c
index cda80ea67..bc3148f54 100644
--- a/crypto/cpu-intel.c
+++ b/crypto/cpu-intel.c
@@ -66,7 +66,14 @@
 #include <stdio.h>
 #include <inttypes.h>
 
-uint32_t OPENSSL_ia32cap_P[4];
+/* This value must be explicitly initialised to zero in order to work around a
+ * bug in libtool or the linker on OS X.
+ *
+ * If not initialised then it becomes a "common symbol". When put into an
+ * archive, linking on OS X will fail to resolve common symbols. By
+ * initialising it to zero, it becomes a "data symbol", which isn't so
+ * affected. */
+uint32_t OPENSSL_ia32cap_P[4] = {0};
 
 /* OPENSSL_ia32_cpuid is defined in cpu-x86_64-asm.pl. */
 extern uint64_t OPENSSL_ia32_cpuid(uint32_t*);
diff --git a/crypto/lhash/lhash_test.c b/crypto/lhash/lhash_test.c
index e53a6f6dd..578bb66f2 100644
--- a/crypto/lhash/lhash_test.c
+++ b/crypto/lhash/lhash_test.c
@@ -12,9 +12,14 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
-#define _POSIX_SOURCE
 #define _BSD_SOURCE
 
+#if !defined(__APPLE__)
+/* _POSIX_SOURCE is needed on Linux in order to get rand_r, but on OS X causes
+ * a build failure. */
+#define _POSIX_SOURCE
+#endif
+
 #include <openssl/lhash.h>
 
 #include <stdio.h>
diff --git a/tool/CMakeLists.txt b/tool/CMakeLists.txt
index d9f673270..4b9c03bc2 100644
--- a/tool/CMakeLists.txt
+++ b/tool/CMakeLists.txt
@@ -10,4 +10,8 @@ add_executable(
 	tool.cc
 )
 
-target_link_libraries(bssl ssl crypto -lrt)
+if (APPLE)
+	target_link_libraries(bssl ssl crypto)
+else()
+	target_link_libraries(bssl ssl crypto -lrt)
+endif()
diff --git a/tool/client.cc b/tool/client.cc
index 6af34a320..5acc8b117 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -17,6 +17,7 @@
 #include <string>
 #include <vector>
 
+#include <errno.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 
diff --git a/tool/speed.cc b/tool/speed.cc
index 176e2e273..8dde77791 100644
--- a/tool/speed.cc
+++ b/tool/speed.cc
@@ -28,6 +28,8 @@
 
 #if defined(OPENSSL_WINDOWS)
 #include <Windows.h>
+#elif defined(OPENSSL_APPLE)
+#include <sys/time.h>
 #endif
 
 extern "C" {
@@ -61,6 +63,17 @@ struct TimeResults {
 
 #if defined(OPENSSL_WINDOWS)
 static uint64_t time_now() { return GetTickCount64() * 1000; }
+#elif defined(OPENSSL_APPLE)
+static uint64_t time_now() {
+  struct timeval tv;
+  uint64_t ret;
+
+  gettimeofday(&tv, NULL);
+  ret = tv.tv_sec;
+  ret *= 1000000;
+  ret += tv.tv_usec;
+  return ret;
+}
 #else
 static uint64_t time_now() {
   struct timespec ts;