diff --git a/build/moz.configure/init.configure b/build/moz.configure/init.configure
index c772604035..891359c5ba 100644
--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -730,6 +730,9 @@ 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 0486cbad1c..d00e2769a5 100644
--- a/js/src/jit/AtomicOperations.h
+++ b/js/src/jit/AtomicOperations.h
@@ -391,7 +391,8 @@ inline bool AtomicOperations::isLockfreeJS(int32_t size) {
 #elif defined(__ppc__) || defined(__PPC__) || defined(__sparc__) ||     \
     defined(__ppc64__) || defined(__PPC64__) || defined(__ppc64le__) || \
     defined(__PPC64LE__) || defined(__alpha__) || defined(__hppa__) ||  \
-    defined(__sh__) || defined(__s390__) || defined(__s390x__)
+    defined(__sh__) || defined(__s390__) || defined(__s390x__) ||       \
+    defined(__riscv)
 #  include "jit/shared/AtomicOperations-feeling-lucky.h"
 #else
 #  error "No AtomicOperations support provided for this platform"
diff --git a/js/src/jit/shared/AtomicOperations-feeling-lucky-gcc.h b/js/src/jit/shared/AtomicOperations-feeling-lucky-gcc.h
index f002cd46c9..e4b6ff9c29 100644
--- a/js/src/jit/shared/AtomicOperations-feeling-lucky-gcc.h
+++ b/js/src/jit/shared/AtomicOperations-feeling-lucky-gcc.h
@@ -70,6 +70,13 @@
 #  endif
 #endif
 
+#ifdef __riscv
+#  if __riscv_xlen == 64
+#    define HAS_64BIT_ATOMICS
+#    define HAS_64BIT_LOCKFREE
+#  endif
+#endif
+
 #ifdef JS_CODEGEN_NONE
 #  ifdef JS_64BIT
 #    define HAS_64BIT_ATOMICS
diff --git a/mfbt/tests/TestPoisonArea.cpp b/mfbt/tests/TestPoisonArea.cpp
index 2834678ad8..381ad08df1 100644
--- a/mfbt/tests/TestPoisonArea.cpp
+++ b/mfbt/tests/TestPoisonArea.cpp
@@ -159,6 +159,14 @@
 #elif defined __aarch64__ || defined _M_ARM64
 #  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];
diff --git a/python/mozbuild/mozbuild/configure/constants.py b/python/mozbuild/mozbuild/configure/constants.py
index 8b7d2261d2..8619421cac 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)