diff --git a/nsprpub/configure b/nsprpub/configure
index 19e9fa60f..619d193ae 100755
--- a/nsprpub/configure
+++ b/nsprpub/configure
@@ -2488,7 +2488,7 @@ test -n "$target_alias" &&
   program_prefix=${target_alias}-
 
 MOD_MAJOR_VERSION=4
-MOD_MINOR_VERSION=18
+MOD_MINOR_VERSION=19
 MOD_PATCH_VERSION=0
 NSPR_MODNAME=nspr20
 _HAVE_PTHREADS=
diff --git a/nsprpub/configure.in b/nsprpub/configure.in
index 7b0b8b395..ea0ae7f8e 100644
--- a/nsprpub/configure.in
+++ b/nsprpub/configure.in
@@ -15,7 +15,7 @@ dnl ========================================================
 dnl = Defaults
 dnl ========================================================
 MOD_MAJOR_VERSION=4
-MOD_MINOR_VERSION=18
+MOD_MINOR_VERSION=19
 MOD_PATCH_VERSION=0
 NSPR_MODNAME=nspr20
 _HAVE_PTHREADS=
diff --git a/nsprpub/pr/include/prinit.h b/nsprpub/pr/include/prinit.h
index c55788923..ab3aba208 100644
--- a/nsprpub/pr/include/prinit.h
+++ b/nsprpub/pr/include/prinit.h
@@ -31,9 +31,9 @@ PR_BEGIN_EXTERN_C
 ** The format of the version string is
 **     "<major version>.<minor version>[.<patch level>] [<Beta>]"
 */
-#define PR_VERSION  "4.18"
+#define PR_VERSION  "4.19"
 #define PR_VMAJOR   4
-#define PR_VMINOR   18
+#define PR_VMINOR   19
 #define PR_VPATCH   0
 #define PR_BETA     PR_FALSE
 
diff --git a/nsprpub/pr/src/md/unix/unix.c b/nsprpub/pr/src/md/unix/unix.c
index 29e24e574..7c90b5075 100644
--- a/nsprpub/pr/src/md/unix/unix.c
+++ b/nsprpub/pr/src/md/unix/unix.c
@@ -2713,8 +2713,13 @@ static void* _MD_Unix_mmap64(
 }  /* _MD_Unix_mmap64 */
 #endif /* defined(_PR_NO_LARGE_FILES) || defined(SOLARIS2_5) */
 
-/* Android <= 19 doesn't have mmap64. */
-#if defined(ANDROID) && __ANDROID_API__ <= 19
+/* NDK non-unified headers for API < 21 don't have mmap64. However,
+ * NDK unified headers do provide mmap64 for all API versions when building
+ * with clang. Therefore, we should provide mmap64 here for API < 21 if we're
+ * not using clang or if we're using non-unified headers. We check for
+ * non-unified headers by the lack of __ANDROID_API_L__ macro. */
+#if defined(ANDROID) && __ANDROID_API__ < 21 && \
+    (!defined(__clang__) || !defined(__ANDROID_API_L__))
 PR_IMPORT(void) *__mmap2(void *, size_t, int, int, int, size_t);
 
 #define ANDROID_PAGE_SIZE 4096
@@ -2784,9 +2789,9 @@ static void _PR_InitIOV(void)
     _md_iovector._stat64 = stat;
     _md_iovector._lseek64 = _MD_Unix_lseek64;
 #elif defined(_PR_HAVE_OFF64_T)
-#if defined(IRIX5_3) || defined(ANDROID)
+#if defined(IRIX5_3) || (defined(ANDROID) && __ANDROID_API__ < 21)
     /*
-     * Android doesn't have open64.  We pass the O_LARGEFILE flag to open
+     * Android < 21 doesn't have open64.  We pass the O_LARGEFILE flag to open
      * in _MD_open.
      */
     _md_iovector._open64 = open;
@@ -2794,8 +2799,14 @@ static void _PR_InitIOV(void)
     _md_iovector._open64 = open64;
 #endif
     _md_iovector._mmap64 = mmap64;
+#if (defined(ANDROID) && __ANDROID_API__ < 21)
+    /* Same as the open64 case for Android. */
+    _md_iovector._fstat64 = fstat;
+    _md_iovector._stat64 = stat;
+#else
     _md_iovector._fstat64 = fstat64;
     _md_iovector._stat64 = stat64;
+#endif
     _md_iovector._lseek64 = lseek64;
 #elif defined(_PR_HAVE_LARGE_OFF_T)
     _md_iovector._open64 = open;
diff --git a/nsprpub/pr/src/pthreads/ptthread.c b/nsprpub/pr/src/pthreads/ptthread.c
index 6046d5d8d..e61a4cbde 100644
--- a/nsprpub/pr/src/pthreads/ptthread.c
+++ b/nsprpub/pr/src/pthreads/ptthread.c
@@ -978,7 +978,23 @@ void _PR_InitThreads(
  * GCC supports the constructor and destructor attributes as of
  * version 2.5.
  */
+#if defined(DARWIN)
+/*
+ * The dynamic linker on OSX doesn't execute __attribute__((destructor))
+ * destructors in the right order wrt non-__attribute((destructor)) destructors
+ * in other libraries. So use atexit() instead, which does.
+ * See https://bugzilla.mozilla.org/show_bug.cgi?id=1399746#c99
+ */
+static void _PR_Fini(void);
+
+__attribute__ ((constructor))
+static void _register_PR_Fini() {
+  atexit(_PR_Fini);
+}
+#else
 static void _PR_Fini(void) __attribute__ ((destructor));
+#endif
+
 #elif defined(__SUNPRO_C)
 /*
  * Sun Studio compiler
diff --git a/nsprpub/pr/tests/prfz.c b/nsprpub/pr/tests/prfz.c
index 0c5a4324f..7179dbecd 100644
--- a/nsprpub/pr/tests/prfz.c
+++ b/nsprpub/pr/tests/prfz.c
@@ -10,6 +10,7 @@
 #include <sys/types.h>
 #include <limits.h>
 #include <string.h>
+#include <stdint.h>
 
 int
 main(int argc, char **argv)
diff --git a/nsprpub/pr/tests/vercheck.c b/nsprpub/pr/tests/vercheck.c
index da2f7b1de..43b0abc4b 100644
--- a/nsprpub/pr/tests/vercheck.c
+++ b/nsprpub/pr/tests/vercheck.c
@@ -40,7 +40,7 @@ static char *compatible_version[] = {
     "4.10", "4.10.1", "4.10.2", "4.10.3", "4.10.4",
     "4.10.5", "4.10.6", "4.10.7", "4.10.8", "4.10.9",
     "4.10.10", "4.11", "4.12", "4.13", "4.14", "4.15",
-    "4.16", "4.17",
+    "4.16", "4.17", "4.18",
     PR_VERSION
 };
 
@@ -56,8 +56,8 @@ static char *incompatible_version[] = {
     "3.0", "3.0.1",
     "3.1", "3.1.1", "3.1.2", "3.1.3",
     "3.5", "3.5.1",
-    "4.18.1",
-    "4.19", "4.19.1",
+    "4.19.1",
+    "4.20", "4.20.1",
     "10.0", "11.1", "12.14.20"
 };
 
