diff --git a/build/moz.configure/init.configure b/build/moz.configure/init.configure
index 83b8d7055..200ea47e5 100644
--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -673,6 +673,9 @@ def split_triplet(triplet, allow_unknown=False):
     elif cpu.startswith('aarch64'):
         canonical_cpu = 'aarch64'
         endianness = 'little'
+    elif cpu.startswith('riscv64'):
+        canonical_cpu = 'riscv64'
+        endianness = 'little'
     elif cpu == 'sh4':
         canonical_cpu = 'sh4'
         endianness = 'little'
diff --git a/js/src/jit/AtomicOperations.h b/js/src/jit/AtomicOperations.h
index 3501e65b8..fda0b1487 100644
--- a/js/src/jit/AtomicOperations.h
+++ b/js/src/jit/AtomicOperations.h
@@ -393,6 +393,8 @@ inline bool AtomicOperations::isLockfreeJS(int32_t size) {
 #include "jit/none/AtomicOperations-feeling-lucky.h"
 #elif defined(__s390__) || defined(__s390x__)
 #include "jit/none/AtomicOperations-feeling-lucky.h"
+#elif defined(__riscv)
+#include "jit/none/AtomicOperations-feeling-lucky.h"
 #else
 #error "No AtomicOperations support provided for this platform"
 #endif
diff --git a/js/src/jit/none/AtomicOperations-feeling-lucky.h b/js/src/jit/none/AtomicOperations-feeling-lucky.h
index c0b436995..f0e2d7150 100644
--- a/js/src/jit/none/AtomicOperations-feeling-lucky.h
+++ b/js/src/jit/none/AtomicOperations-feeling-lucky.h
@@ -80,6 +80,14 @@
 #define GNUC_COMPATIBLE
 #endif
 
+#ifdef __riscv
+#  define GNUC_COMPATIBLE
+#  if __riscv_xlen == 64
+#    define HAS_64BIT_ATOMICS
+#    define HAS_64BIT_LOCKFREE
+#  endif
+#endif
+
 // The default implementation tactic for gcc/clang is to use the newer
 // __atomic intrinsics added for use in C++11 <atomic>.  Where that
 // isn't available, we use GCC's older __sync functions instead.
diff --git a/mfbt/tests/TestPoisonArea.cpp b/mfbt/tests/TestPoisonArea.cpp
index 06c24ed03..708ea558e 100644
--- a/mfbt/tests/TestPoisonArea.cpp
+++ b/mfbt/tests/TestPoisonArea.cpp
@@ -160,6 +160,14 @@
 #elif defined __aarch64__
 #define RETURN_INSTR 0xd65f03c0 /* ret */
 
+#elif defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen == 64
+#if defined(__riscv_compressed)
+#define RETURN_INSTR 0x8082 /* ret */
+#define RETURN_INSTR_TYPE uint16_t
+#else
+#define RETURN_INSTR 0x00008067 /* ret */
+#endif
+
 #elif defined __ia64
 struct ia64_instr { uint32_t mI[4]; };
 static const ia64_instr _return_instr =
diff --git a/python/mozbuild/mozbuild/configure/constants.py b/python/mozbuild/mozbuild/configure/constants.py
index 33ae5a456..3edb0d618 100644
--- a/python/mozbuild/mozbuild/configure/constants.py
+++ b/python/mozbuild/mozbuild/configure/constants.py
@@ -50,6 +50,7 @@ CPU_bitness = {
     'mips64': 64,
     'ppc': 32,
     'ppc64': 64,
+    'riscv64': 64,
     's390': 32,
     's390x': 64,
     'sh4': 32,
@@ -89,6 +90,7 @@ CPU_preprocessor_checks = OrderedDict((
     ('mips64', '__mips64'),
     ('mips32', '__mips__'),
     ('sh4', '__sh__'),
+    ('riscv64', 'defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen == 64'),
 ))
 
 assert sorted(CPU_preprocessor_checks.keys()) == sorted(CPU.POSSIBLE_VALUES)