diff --git a/c/include/cccl/reduce.h b/c/include/cccl/c/reduce.h
similarity index 85%
rename from c/include/cccl/reduce.h
rename to c/include/cccl/c/reduce.h
index 5047625a85..1da7b51f01 100644
--- a/c/include/cccl/reduce.h
+++ b/c/include/cccl/c/reduce.h
@@ -11,12 +11,12 @@
 #pragma once
 
 #ifndef CCCL_C_EXPERIMENTAL
-#  warning "C exposure is experimental and subject to change. Define CCCL_C_EXPERIMENTAL to acknowledge this warning."
-#else // ^^^ !CCCL_C_EXPERIMENTAL ^^^ / vvv CCCL_C_EXPERIMENTAL vvv
+#  error "C exposure is experimental and subject to change. Define CCCL_C_EXPERIMENTAL to acknowledge this notice."
+#endif // !CCCL_C_EXPERIMENTAL
 
-#  include <cuda.h>
+#include <cuda.h>
 
-#  include <cccl/types.h>
+#include <cccl/c/types.h>
 
 struct cccl_device_reduce_build_result_t
 {
@@ -55,5 +55,3 @@ extern "C" CCCL_C_API CUresult cccl_device_reduce(
   CUstream stream) noexcept;
 
 extern "C" CCCL_C_API CUresult cccl_device_reduce_cleanup(cccl_device_reduce_build_result_t* bld_ptr);
-
-#endif // CCCL_C_EXPERIMENTAL
diff --git a/c/include/cccl/types.h b/c/include/cccl/c/types.h
similarity index 78%
rename from c/include/cccl/types.h
rename to c/include/cccl/c/types.h
index 781b9f9ea6..f34466c755 100644
--- a/c/include/cccl/types.h
+++ b/c/include/cccl/c/types.h
@@ -11,14 +11,14 @@
 #pragma once
 
 #ifndef CCCL_C_EXPERIMENTAL
-#  warning "C exposure is experimental and subject to change. Define CCCL_C_EXPERIMENTAL to acknowledge this warning."
-#else // ^^^ !CCCL_C_EXPERIMENTAL ^^^ / vvv CCCL_C_EXPERIMENTAL vvv
+#  error "C exposure is experimental and subject to change. Define CCCL_C_EXPERIMENTAL to acknowledge this notice."
+#endif // !CCCL_C_EXPERIMENTAL
 
-#  if defined(_WIN32)
-#    define CCCL_C_API __declspec(dllexport)
-#  else
-#    define CCCL_C_API __attribute__((visibility("default")))
-#  endif
+#if defined(_WIN32)
+#  define CCCL_C_API __declspec(dllexport)
+#else // ^^^ _WIN32 ^^^ / vvv !_WIN32 vvv
+#  define CCCL_C_API __attribute__((visibility("default")))
+#endif // !_WIN32
 
 enum class cccl_type_enum
 {
@@ -81,5 +81,3 @@ struct cccl_iterator_t
   cccl_type_info value_type;
   void* state;
 };
-
-#endif // CCCL_C_EXPERIMENTAL
diff --git a/c/src/reduce.cu b/c/src/reduce.cu
index 4badcd1ff0..fc88dd31a9 100644
--- a/c/src/reduce.cu
+++ b/c/src/reduce.cu
@@ -19,7 +19,7 @@
 #include <iostream>
 #include <memory>
 
-#include <cccl/reduce.h>
+#include <cccl/c/reduce.h>
 #include <nvJitLink.h>
 #include <nvrtc.h>
 
diff --git a/c/test/c2h.h b/c/test/c2h.h
index e2b26895a8..e044d2e17a 100644
--- a/c/test/c2h.h
+++ b/c/test/c2h.h
@@ -23,7 +23,7 @@
 #include <vector>
 
 #include <catch2/catch.hpp>
-#include <cccl/reduce.h>
+#include <cccl/c/reduce.h>
 #include <nvrtc.h>
 
 static std::string inspect_sass(const void* cubin, size_t cubin_size)