diff --git a/R-package/configure b/R-package/configure
index 11d691674f69..24ef441c02d5 100755
--- a/R-package/configure
+++ b/R-package/configure
@@ -1789,7 +1789,7 @@ ${CXX} ${CPPFLAGS} ${CXXFLAGS} -o conftest conftest.cpp 2>/dev/null && ./conftes
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: ${ac_mmprefetch}" >&5
 printf "%s\n" "${ac_mmprefetch}" >&6; }
 if test "${ac_mmprefetch}" = yes; then
-    LGB_CPPFLAGS+=" -DMM_PREFETCH=1"
+    LGB_CPPFLAGS="${LGB_CPPFLAGS} -DMM_PREFETCH=1"
 fi
 
 ############
@@ -1824,7 +1824,7 @@ ${CXX} ${CPPFLAGS} ${CXXFLAGS} -o conftest conftest.cpp 2>/dev/null && ./conftes
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: ${ac_mm_malloc}" >&5
 printf "%s\n" "${ac_mm_malloc}" >&6; }
 if test "${ac_mm_malloc}" = yes; then
-    LGB_CPPFLAGS+=" -DMM_MALLOC=1"
+    LGB_CPPFLAGS="${LGB_CPPFLAGS} -DMM_MALLOC=1"
 fi
 
 ##########
diff --git a/R-package/configure.ac b/R-package/configure.ac
index dad365be691c..8cc1c522b179 100644
--- a/R-package/configure.ac
+++ b/R-package/configure.ac
@@ -60,7 +60,7 @@ AC_LANG_CONFTEST(
 ${CXX} ${CPPFLAGS} ${CXXFLAGS} -o conftest conftest.cpp 2>/dev/null && ./conftest && ac_mmprefetch=yes
 AC_MSG_RESULT([${ac_mmprefetch}])
 if test "${ac_mmprefetch}" = yes; then
-    LGB_CPPFLAGS+=" -DMM_PREFETCH=1"
+    LGB_CPPFLAGS="${LGB_CPPFLAGS} -DMM_PREFETCH=1"
 fi
 
 ############
@@ -86,7 +86,7 @@ AC_LANG_CONFTEST(
 ${CXX} ${CPPFLAGS} ${CXXFLAGS} -o conftest conftest.cpp 2>/dev/null && ./conftest && ac_mm_malloc=yes
 AC_MSG_RESULT([${ac_mm_malloc}])
 if test "${ac_mm_malloc}" = yes; then
-    LGB_CPPFLAGS+=" -DMM_MALLOC=1"
+    LGB_CPPFLAGS="${LGB_CPPFLAGS} -DMM_MALLOC=1"
 fi
 
 ##########