diff --git a/glslang/CMakeLists.txt b/glslang/CMakeLists.txt
index 38b0a983..7fa55660 100644
--- a/glslang/CMakeLists.txt
+++ b/glslang/CMakeLists.txt
@@ -68,19 +68,18 @@ set(HEADERS
     MachineIndependent/preprocessor/PpTokens.h)
 
 find_package(BISON)
-if(BISON_FOUND)
-    message("bison found")
-    BISON_TARGET(GLSLParser MachineIndependent/glslang.y ${CMAKE_CURRENT_BINARY_DIR}/gen_glslang_tab.cpp
-                 COMPILE_FLAGS
-                 "--defines=${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp.h")
-else(BISON_FOUND)
-    message("using custom command for bison on glslang.y")
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp.h
-                       COMMAND ../tools/bison.exe --defines=${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp.h -t MachineIndependent/glslang.y -o ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp
-                       MAIN_DEPENDENCY MachineIndependent/glslang.y
-                       WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
-    set(BISON_GLSLParser_OUTPUT_SOURCE ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp)
-endif(BISON_FOUND)
+if(NOT BISON_FOUND)
+    set(BISON_EXECUTABLE ../tools/bison.exe)
+    message("bison not found. Assuming it is at ${BISON_EXECUTABLE}")
+endif()
+
+# Always use a custom command since our use of --defines isn't assumed by CMake's BISON_TARGET,
+# which ends up causing the target to always be rebuilt.
+add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp.h
+                   COMMAND ${BISON_EXECUTABLE} --defines=${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp.h -t MachineIndependent/glslang.y -o ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp
+                   MAIN_DEPENDENCY MachineIndependent/glslang.y
+                   WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+set(BISON_GLSLParser_OUTPUT_SOURCE ${CMAKE_CURRENT_BINARY_DIR}/glslang_tab.cpp)
 
 add_library(glslang STATIC ${BISON_GLSLParser_OUTPUT_SOURCE} ${SOURCES} ${HEADERS})