diff --git a/CMakeLists.txt b/CMakeLists.txt
index 488c85c..50ec5c6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,10 +36,16 @@ include(CheckIPOSupported)
 check_ipo_supported(RESULT ipo_available OUTPUT error LANGUAGES C)
 
 # Enable IPO by default, if available
-if(ipo_available)
-  set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
-else()
-  message(WARNING "IPO is not supported, expect performance penalty")
+if(NOT DEFINED CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+  if(ipo_available)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+  else()
+    message(WARNING "IPO is not supported, disabling")
+  endif()
+endif()
+
+if(NOT CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+  message(WARNING "IPO is not enabled, expect performance penalty")
 endif()
 
 # Extra build type for AddressSanitizer (Asan)
diff --git a/nix/rt.nix b/nix/rt.nix
index c1a3d6c..c829bbd 100644
--- a/nix/rt.nix
+++ b/nix/rt.nix
@@ -92,6 +92,9 @@ let
       stdenv = stdenv;
     }).overrideAttrs (old: {
       pname = old.name + "@" + stdenv.cc.cc.version;
+      cmakeFlags = old.cmakeFlags ++ [
+        "-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=OFF"
+      ];
     });
 
     oldCompilers = [