diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index f8f9af094bd2440d91d7b2797395eba15770dc01..a1e59374ba1a7fc8f9f511320d30a419ad96706b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -34,8 +34,12 @@ endif()
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   ## Some CMake versions use -O2 for release; replace with -O3
-  string(REPLACE "-O2" "-O3" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
-  string(REPLACE "-O2" "-O3" CMAKE_CUDA_FLAGS_RELEASE ${CMAKE_CUDA_FLAGS_RELEASE})
+  if(CMAKE_CXX_FLAGS_RELEASE)
+    string(REPLACE "-O2" "-O3" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
+  endif()
+  if(CMAKE_CUDA_FLAGS_RELEASE)
+    string(REPLACE "-O2" "-O3" CMAKE_CUDA_FLAGS_RELEASE ${CMAKE_CUDA_FLAGS_RELEASE})
+  endif()
 endif()
 
 
diff --git a/src/GrandBrownTown.cu b/src/GrandBrownTown.cu
index d610c5d4404560e981970f3461cbe247982283c3..aa5295f4271f2ac169033e139e2fa15418654562 100644
--- a/src/GrandBrownTown.cu
+++ b/src/GrandBrownTown.cu
@@ -746,7 +746,7 @@ void GrandBrownTown::run()
 
         }//if step == 1
 
-	PUSH_NVTX("Clear particle force data",1)
+	PUSH_NVTX("Clear particle energy data",1)
 	internal->clear_energy();
 	gpuman.sync();
 	POP_NVTX
@@ -1171,6 +1171,7 @@ void GrandBrownTown::run()
                 wkf_timer_start(timerS);
 		POP_NVTX
          } // s % outputEnergyPeriod
+     POP_NVTX
      } // done with all Brownian dynamics steps
 
      if (imd_on and clientsock)