c3-lang/libtommath

diff --git a/tommath_private.h b/tommath_private.h
index b316358..5ceda2e 100644
--- a/tommath_private.h
+++ b/tommath_private.h
@@ -37,7 +37,7 @@ extern "C" {
 do {                                                    \
    size_t fs_ = (size);                                 \
    void* fm_ = (mem);                                   \
-   if (fm_) {                                           \
+   if (fm_ != NULL) {                                   \
       MP_ZERO_BUFFER(fm_, fs_);                         \
       MP_FREE(fm_, fs_);                                \
    }                                                    \
@@ -46,7 +46,7 @@ do {                                                    \
 do {                                                    \
    int fd_ = (digits);                                  \
    void* fm_ = (mem);                                   \
-   if (fm_) {                                           \
+   if (fm_ != NULL) {                                   \
       MP_ZERO_BUFFER(fm_, sizeof(mp_digit) * (size_t)fd_); \
       MP_FREE(fm_, sizeof(mp_digit) * (size_t)fd_);     \
    }                                                    \