diff --git a/pkgs/by-name/is/ispc/package.nix b/pkgs/by-name/is/ispc/package.nix
index e08668ded3f6..56ccceaec1f6 100644
--- a/pkgs/by-name/is/ispc/package.nix
+++ b/pkgs/by-name/is/ispc/package.nix
@@ -15,6 +15,8 @@
   testedTargets ?
     if stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isAarch32 then
       [ "neon-i32x4" ]
+    else if stdenv.hostPlatform.isRiscV64 then
+      [ "rvv-x4" ]
     else
       [ "sse2-i32x4" ],
 }:
@@ -58,6 +60,11 @@ stdenv.mkDerivation (finalAttrs: {
 
   inherit testedTargets;
 
+  # run_tests.py does not know riscv64 hosts and defaults to x86 targets
+  patches = lib.optionals stdenv.hostPlatform.isRiscV64 [
+    ./run-tests-riscv64.patch
+  ];
+
   doCheck = true;
 
   # the compiler enforces -Werror, and -fno-strict-overflow makes it mad.
@@ -87,12 +94,13 @@ stdenv.mkDerivation (finalAttrs: {
     (lib.cmakeFeature "CLANGPP_EXECUTABLE" "${llvmPackages.clang}/bin/clang++")
     (lib.cmakeBool "ISPC_INCLUDE_EXAMPLES" false)
     (lib.cmakeBool "ISPC_INCLUDE_UTILS" false)
-    (lib.cmakeFeature "ARM_ENABLED=" (
+    (lib.cmakeFeature "ARM_ENABLED" (
       if stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isAarch32 then "TRUE" else "FALSE"
     ))
-    (lib.cmakeFeature "X86_ENABLED=" (
+    (lib.cmakeFeature "X86_ENABLED" (
       if stdenv.hostPlatform.isx86_64 || stdenv.hostPlatform.isx86_32 then "TRUE" else "FALSE"
     ))
+    (lib.cmakeFeature "RISCV_ENABLED" (if stdenv.hostPlatform.isRiscV64 then "TRUE" else "FALSE"))
   ];
 
   meta = {
diff --git a/pkgs/by-name/is/ispc/run-tests-riscv64.patch b/pkgs/by-name/is/ispc/run-tests-riscv64.patch
new file mode 100644
index 000000000000..d00240c4ce64
--- /dev/null
+++ b/pkgs/by-name/is/ispc/run-tests-riscv64.patch
@@ -0,0 +1,12 @@
+--- a/scripts/run_tests.py
++++ b/scripts/run_tests.py
+@@ -1368,6 +1368,9 @@
+ elif platform.machine() == "ppc64le":
+     default_target = "generic-i32x4"
+     default_arch = "ppc64le"
++elif platform.machine() == "riscv64":
++    default_target = "rvv-x4"
++    default_arch = "riscv64"
+ elif "86" in platform.machine() or platform.machine() == "AMD64":
+     # Some variant of x86: x86_64, i386, i486, i586, i686
+     # Windows reports platform as AMD64