diff --git a/build_files/build_environment/cmake/osl.cmake b/build_files/build_environment/cmake/osl.cmake
index f629c964908..f8a1d781486 100644
--- a/build_files/build_environment/cmake/osl.cmake
+++ b/build_files/build_environment/cmake/osl.cmake
@@ -77,9 +77,13 @@ ExternalProject_Add(external_osl
   URL_HASH ${OSL_HASH_TYPE}=${OSL_HASH}
   PREFIX ${BUILD_DIR}/osl
 
-  PATCH_COMMAND ${PATCH_CMD} -p 1 -d
-    ${BUILD_DIR}/osl/src/external_osl <
-    ${PATCH_DIR}/osl.diff
+  PATCH_COMMAND
+    ${PATCH_CMD} -p 1 -d
+      ${BUILD_DIR}/osl/src/external_osl <
+      ${PATCH_DIR}/osl.diff &&
+    ${PATCH_CMD} -p 1 -d
+      ${BUILD_DIR}/osl/src/external_osl <
+      ${PATCH_DIR}/osl_supports_isa_thread.diff
 
   CMAKE_ARGS
     -DCMAKE_INSTALL_PREFIX=${LIBDIR}/osl
diff --git a/build_files/build_environment/patches/osl_supports_isa_thread.diff b/build_files/build_environment/patches/osl_supports_isa_thread.diff
new file mode 100644
index 00000000000..6d1886aef4c
--- /dev/null
+++ b/build_files/build_environment/patches/osl_supports_isa_thread.diff
@@ -0,0 +1,48 @@
+From 69d11b6eebcfb1501193184333280ebd5985564e Mon Sep 17 00:00:00 2001
+From: Sergey Sharybin <sergey@blender.org>
+Date: Thu, 9 Oct 2025 12:25:09 +0200
+Subject: [PATCH] Fix: LLVM_Util::supports_isa is not thread-safe
+
+The supports_isa() function might be called from threads, and prior
+to this change it might have added entries to the global sCpuFeatures
+variable. This happened when detect_cpu_features() is called with
+TargetISA::UNKNOWN and the code was looking for the best ISA. This
+could lead to situation when the host CPU is ARM, and the probing
+happens for AVX512.
+
+This change ensures that the supports_isa() accesses sCpuFeatures
+in the read-only manner.
+
+This was originally noticed as unreliable OSL render tests in Blender
+reported at https://projects.blender.org/blender/blender/issues/147642
+
+Signed-off-by: Sergey Sharybin <sergey@blender.org>
+---
+ src/liboslexec/llvm_util.cpp | 11 ++++++++++-
+ 1 file changed, 10 insertions(+), 1 deletion(-)
+
+diff --git a/src/liboslexec/llvm_util.cpp b/src/liboslexec/llvm_util.cpp
+index f9b1296d..2d952567 100644
+--- a/src/liboslexec/llvm_util.cpp
++++ b/src/liboslexec/llvm_util.cpp
+@@ -1443,7 +1443,16 @@ LLVM_Util::supports_isa(TargetISA target)
+             continue;
+         }
+         OSL_DEV_ONLY(std::cout << "Testing for cpu feature:" << f << std::endl);
+-        if (sCpuFeatures[f] == false) {
++        // The required CPU feature for the specified target might not be in
++        // the sCpuFeatures. This happens, for example, when the code is probing
++        // the best target ISA when the requested one is UNKNOWN. In this case
++        // it is possible that this function is called for the TargetISA::AVX512
++        // on an ARM CPU.
++        // This function might be called from multiple threads, so it is important
++        // to keep the access to sCpuFeatures read-only.
++        const auto cpu_feature_it = sCpuFeatures.find(f);
++        if (cpu_feature_it == sCpuFeatures.end()
++            || cpu_feature_it->second == false) {
+             OSL_DEV_ONLY(std::cout << "MISSING cpu feature:" << f << std::endl);
+             return false;
+         }
+-- 
+2.51.0
+