diff --git a/build.rs b/build.rs
index c6cb3a700..62b150170 100644
--- a/build.rs
+++ b/build.rs
@@ -65,6 +65,7 @@ const RING_SRCS: &[(&[&str], &str)] = &[
     (&[], "third_party/fiat/curve25519.c"),
 
     (&[X86_64, X86], "crypto/cpu-intel.c"),
+    (&[AARCH64], "crypto/cpu-aarch64.c"),
 
     (&[X86], "crypto/fipsmodule/aes/asm/aes-586.pl"),
     (&[X86], "crypto/fipsmodule/aes/asm/aesni-x86.pl"),
diff --git a/crypto/cpu-aarch64.c b/crypto/cpu-aarch64.c
new file mode 100644
index 000000000..263c5b866
--- /dev/null
+++ b/crypto/cpu-aarch64.c
@@ -0,0 +1,46 @@
+// Copyright 2019 Greg V
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+
+// Run-time feature detection for aarch64 on any OS that emulates the mrs instruction.
+//
+// On FreeBSD >= 12.0, Linux >= 4.11 and other operating systems, it is possible to use
+// privileged system registers from userspace to check CPU feature support.
+//
+// For proper support of SoCs where different cores have different capabilities
+// the OS has to always report only the features supported by all cores, like FreeBSD does.
+//
+// Only FreeBSD uses this right now.
+
+#ifdef __FreeBSD__
+#pragma GCC diagnostic ignored "-Wgnu-statement-expression"
+#include <GFp/cpu.h>
+#include <GFp/arm_arch.h>
+#include <machine/armreg.h>
+
+void GFp_mrs_setup(void) {
+  GFp_armcap_P = 0;
+
+  uint64_t id_aa64isar0 = READ_SPECIALREG(ID_AA64ISAR0_EL1);
+
+  if (ID_AA64ISAR0_AES(id_aa64isar0) >= ID_AA64ISAR0_AES_BASE)
+    GFp_armcap_P |= ARMV8_AES;
+
+  if (ID_AA64ISAR0_AES(id_aa64isar0) >= ID_AA64ISAR0_AES_PMULL)
+    GFp_armcap_P |= ARMV8_PMULL;
+
+  if (ID_AA64ISAR0_SHA2(id_aa64isar0) >= ID_AA64ISAR0_SHA2_BASE)
+    GFp_armcap_P |= ARMV8_SHA256;
+}
+#endif
diff --git a/include/GFp/arm_arch.h b/include/GFp/arm_arch.h
index ee5e32c8f..822783ebb 100644
--- a/include/GFp/arm_arch.h
+++ b/include/GFp/arm_arch.h
@@ -107,7 +107,13 @@
 // ARMV7_NEON is true when a NEON unit is present in the current CPU.
 #define ARMV7_NEON (1 << 0)
 
+// ARMV8_AES indicates support for hardware AES instructions.
+#define ARMV8_AES (1 << 2)
+
 // ARMV8_SHA256 indicates support for hardware SHA-256 instructions.
 #define ARMV8_SHA256 (1 << 4)
 
+// ARMV8_PMULL indicates support for hardware polynomial multiply instructions.
+#define ARMV8_PMULL (1 << 5)
+
 #endif  // OPENSSL_HEADER_ARM_ARCH_H
diff --git a/include/GFp/cpu.h b/include/GFp/cpu.h
index 462018afa..96a4917c9 100644
--- a/include/GFp/cpu.h
+++ b/include/GFp/cpu.h
@@ -89,4 +89,11 @@
 extern uint32_t GFp_ia32cap_P[4];
 #endif
 
+#if defined(OPENSSL_ARM) || defined(OPENSSL_AARCH64)
+// GFp_armcap_P contains feature flags when running on an ARM system.
+//
+// The flags are defined in <GFp/arm_arch.h>.
+extern uint32_t GFp_armcap_P;
+#endif
+
 #endif  // OPENSSL_HEADER_CPU_H
diff --git a/src/cpu.rs b/src/cpu.rs
index bfd87c8de..d997f7223 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -60,6 +60,16 @@ pub(crate) fn features() -> Features {
             {
                 arm::fuchsia_setup();
             }
+
+            #[cfg(all(any(target_os = "freebsd"), target_arch = "aarch64"))]
+            {
+                extern "C" {
+                    fn GFp_mrs_setup();
+                }
+                unsafe {
+                    GFp_mrs_setup();
+                }
+            }
         });
     }
 
@@ -171,7 +181,7 @@ pub(crate) mod arm {
     pub(crate) struct Feature {
         #[cfg_attr(
             not(all(
-                any(target_os = "android", target_os = "linux", target_os = "fuchsia"),
+                any(target_os = "android", all(target_os = "freebsd", target_arch = "aarch64"), target_os = "linux", target_os = "fuchsia"),
                 any(target_arch = "arm", target_arch = "aarch64")
             )),
             allow(dead_code)
@@ -191,7 +201,7 @@ pub(crate) mod arm {
             }
 
             #[cfg(all(
-                any(target_os = "android", target_os = "linux", target_os = "fuchsia"),
+                any(target_os = "android", all(target_os = "freebsd", target_arch = "aarch64"), target_os = "linux", target_os = "fuchsia"),
                 any(target_arch = "arm", target_arch = "aarch64")
             ))]
             {
@@ -199,7 +209,7 @@ pub(crate) mod arm {
             }
 
             #[cfg(not(all(
-                any(target_os = "android", target_os = "ios", target_os = "linux", target_os = "fuchsia"),
+                any(target_os = "android", all(target_os = "freebsd", target_arch = "aarch64"), target_os = "ios", target_os = "linux", target_os = "fuchsia"),
                 any(target_arch = "arm", target_arch = "aarch64")
             )))]
             {
@@ -231,7 +241,7 @@ pub(crate) mod arm {
     };
 
     #[cfg(all(
-        any(target_os = "android", target_os = "linux", target_os = "fuchsia"),
+        any(target_os = "android", all(target_os = "freebsd", target_arch = "aarch64"), target_os = "linux", target_os = "fuchsia"),
         any(target_arch = "arm", target_arch = "aarch64")
     ))]
     extern "C" {