diff --git a/Utilities/cmliblzma/CMakeLists.txt b/Utilities/cmliblzma/CMakeLists.txt
index d991438d6..89205366f 100644
--- a/Utilities/cmliblzma/CMakeLists.txt
+++ b/Utilities/cmliblzma/CMakeLists.txt
@@ -211,4 +211,14 @@ ENDIF()
 
 ADD_LIBRARY(cmliblzma ${LZMA_SRCS})
 
+IF(CMAKE_C_COMPILER_ID STREQUAL "XL")
+  # Disable the XL compiler optimizer because it causes crashes
+  # and other bad behavior in liblzma code.
+  SET_PROPERTY(TARGET cmliblzma PROPERTY COMPILE_FLAGS "-qnooptimize")
+ELSEIF(CMAKE_C_COMPILER_ID STREQUAL "GNU" AND
+       CMAKE_C_COMPILER_VERSION VERSION_LESS 3.4)
+  # Disable the old GNU compiler optimizer.
+  SET_PROPERTY(TARGET cmliblzma PROPERTY COMPILE_FLAGS "-O0")
+ENDIF()
+
 INSTALL(FILES COPYING DESTINATION ${CMAKE_DOC_DIR}/cmliblzma)
diff --git a/Utilities/cmliblzma/liblzma/lzma/lzma_encoder_optimum_normal.c b/Utilities/cmliblzma/liblzma/lzma/lzma_encoder_optimum_normal.c
index fc54d8d31..d3a63485c 100644
--- a/Utilities/cmliblzma/liblzma/lzma/lzma_encoder_optimum_normal.c
+++ b/Utilities/cmliblzma/liblzma/lzma/lzma_encoder_optimum_normal.c
@@ -8,9 +8,6 @@
 //  You can do whatever you want with this file.
 //
 ///////////////////////////////////////////////////////////////////////////////
-#if defined(__IBMC__)
-# pragma options optimize=0
-#endif
 
 #include "lzma_encoder_private.h"
 #include "fastpos.h"