diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1d1efe55..4782923a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,7 +84,6 @@ endif()
 
 # OpenMP
 if(USE_OPENMP)
-  add_definitions(-DSTOCHTREE_OPENMP_AVAILABLE)
   if(APPLE)
     find_package(OpenMP)
     if(NOT OpenMP_FOUND)
diff --git a/configure b/configure
index 2480c9a9..bdffbd87 100755
--- a/configure
+++ b/configure
@@ -608,7 +608,6 @@ PACKAGE_URL=''
 ac_subst_vars='LTLIBOBJS
 LIBOBJS
 STOCHTREE_CPPFLAGS
-OPENMP_AVAILABILITY_FLAGS
 OPENMP_LIB
 OPENMP_CXXFLAGS
 target_alias
@@ -1762,14 +1761,12 @@ OPENMP_CXXFLAGS=""
 if test `uname -s` = "Linux"
 then
     OPENMP_CXXFLAGS="\$(SHLIB_OPENMP_CXXFLAGS)"
-    OPENMP_AVAILABILITY_FLAGS='-DSTOCHTREE_OPENMP_AVAILABLE'
 fi
 
 if test `uname -s` = "Darwin"
 then
     OPENMP_CXXFLAGS='-Xclang -fopenmp'
     OPENMP_LIB='-lomp'
-    OPENMP_AVAILABILITY_FLAGS='-DSTOCHTREE_OPENMP_AVAILABLE'
 
     # libomp 15.0+ from brew is keg-only (i.e. not symlinked into the standard paths search by the linker),
     # so need to search in other locations.
@@ -1830,7 +1827,6 @@ printf "%s\n" "${ac_pkg_openmp}" >&6; }
     if test "${ac_pkg_openmp}" = no; then
         OPENMP_CXXFLAGS=''
         OPENMP_LIB=''
-        OPENMP_AVAILABILITY_FLAGS=''
         echo '***********************************************************************************************'
         echo ' OpenMP is unavailable on this macOS system. stochtree code will run single-threaded as a result.'
         echo ' To use all CPU cores for training jobs, you should install OpenMP by running'
@@ -1844,7 +1840,6 @@ fi
 
 
 
-
 ac_config_files="$ac_config_files src/Makevars"
 
 
diff --git a/configure.ac b/configure.ac
index c329eeb3..ae8a9f7f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -47,14 +47,12 @@ OPENMP_CXXFLAGS=""
 if test `uname -s` = "Linux"
 then
     OPENMP_CXXFLAGS="\$(SHLIB_OPENMP_CXXFLAGS)"
-    OPENMP_AVAILABILITY_FLAGS='-DSTOCHTREE_OPENMP_AVAILABLE'
 fi
 
 if test `uname -s` = "Darwin"
 then
     OPENMP_CXXFLAGS='-Xclang -fopenmp'
     OPENMP_LIB='-lomp'
-    OPENMP_AVAILABILITY_FLAGS='-DSTOCHTREE_OPENMP_AVAILABLE'
 
     # libomp 15.0+ from brew is keg-only (i.e. not symlinked into the standard paths search by the linker),
     # so need to search in other locations.
@@ -104,7 +102,6 @@ then
     if test "${ac_pkg_openmp}" = no; then
         OPENMP_CXXFLAGS=''
         OPENMP_LIB=''
-        OPENMP_AVAILABILITY_FLAGS=''
         echo '***********************************************************************************************'
         echo ' OpenMP is unavailable on this macOS system. stochtree code will run single-threaded as a result.'
         echo ' To use all CPU cores for training jobs, you should install OpenMP by running'
@@ -117,7 +114,6 @@ fi
 # substitute variables from this script into Makevars.in
 AC_SUBST(OPENMP_CXXFLAGS)
 AC_SUBST(OPENMP_LIB)
-AC_SUBST(OPENMP_AVAILABILITY_FLAGS)
 AC_SUBST(STOCHTREE_CPPFLAGS)
 AC_CONFIG_FILES([src/Makevars])
 
diff --git a/configure.win b/configure.win
index 4bc2a539..cf9efa4a 100644
--- a/configure.win
+++ b/configure.win
@@ -26,7 +26,7 @@ STOCHTREE_CPPFLAGS="${STOCHTREE_CPPFLAGS} -DEIGEN_MPL2_ONLY -DEIGEN_DONT_PARALLE
 # OpenMP #
 ##########
 
-STOCHTREE_CPPFLAGS="${STOCHTREE_CPPFLAGS} -DSTOCHTREE_OPENMP_AVAILABLE"
+STOCHTREE_CPPFLAGS="${STOCHTREE_CPPFLAGS}"
 
 #########################
 # Generate Makevars.win #
diff --git a/include/stochtree/openmp_utils.h b/include/stochtree/openmp_utils.h
index 28ed31fb..78c17234 100644
--- a/include/stochtree/openmp_utils.h
+++ b/include/stochtree/openmp_utils.h
@@ -6,7 +6,7 @@
 
 namespace StochTree {
 
-#ifdef STOCHTREE_OPENMP_AVAILABLE
+#ifdef _OPENMP
 
 #include <omp.h>
 #define STOCHTREE_HAS_OPENMP 1
@@ -40,7 +40,6 @@ inline void set_num_threads(int num_threads) {
 #else
 #define STOCHTREE_HAS_OPENMP 0
 
-// Fallback implementations when OpenMP is not available
 inline int get_max_threads() {return 1;}
 
 inline int get_thread_num() {return 0;}
diff --git a/src/Makevars.in b/src/Makevars.in
index 4eb970cb..1ebed5de 100644
--- a/src/Makevars.in
+++ b/src/Makevars.in
@@ -4,7 +4,6 @@ PKGROOT=..
 
 STOCHTREE_CPPFLAGS = \
     @STOCHTREE_CPPFLAGS@ \
-    @OPENMP_AVAILABILITY_FLAGS@ \
     -DSTOCHTREE_R_BUILD
 
 PKG_CPPFLAGS = \