diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9191829a83..6fd7dfb771 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   * Fixed a flattening issue for certain complex `map` nestings
     (#1168).
 
+  * Made API function `futhark_context_clear_caches()` thread safe
+    (#1169).
+
 ## [0.18.1]
 
 ### Added
diff --git a/src/Futhark/CodeGen/Backends/CCUDA/Boilerplate.hs b/src/Futhark/CodeGen/Backends/CCUDA/Boilerplate.hs
index b810f6b4bb..0dea262848 100644
--- a/src/Futhark/CodeGen/Backends/CCUDA/Boilerplate.hs
+++ b/src/Futhark/CodeGen/Backends/CCUDA/Boilerplate.hs
@@ -461,7 +461,9 @@ generateContextFuns cfg cost_centres kernels sizes failures = do
   GC.publicDef_ "context_clear_caches" GC.MiscDecl $ \s ->
     ( [C.cedecl|int $id:s(struct $id:ctx* ctx);|],
       [C.cedecl|int $id:s(struct $id:ctx* ctx) {
+                         lock_lock(&ctx->lock);
                          CUDA_SUCCEED(cuda_free_all(&ctx->cuda));
+                         lock_unlock(&ctx->lock);
                          return 0;
                        }|]
     )
diff --git a/src/Futhark/CodeGen/Backends/COpenCL/Boilerplate.hs b/src/Futhark/CodeGen/Backends/COpenCL/Boilerplate.hs
index b4b15c0a72..bc8325d6ad 100644
--- a/src/Futhark/CodeGen/Backends/COpenCL/Boilerplate.hs
+++ b/src/Futhark/CodeGen/Backends/COpenCL/Boilerplate.hs
@@ -492,7 +492,9 @@ generateBoilerplate opencl_code opencl_prelude cost_centres kernels types sizes
   GC.publicDef_ "context_clear_caches" GC.MiscDecl $ \s ->
     ( [C.cedecl|int $id:s(struct $id:ctx* ctx);|],
       [C.cedecl|int $id:s(struct $id:ctx* ctx) {
+                         lock_lock(&ctx->lock);
                          ctx->error = OPENCL_SUCCEED_NONFATAL(opencl_free_all(&ctx->opencl));
+                         lock_unlock(&ctx->lock);
                          return ctx->error != NULL;
                        }|]
     )