diff --git a/src/coalesce.c b/src/coalesce.c
index 70a0d0999a..0a0c3e393f 100644
--- a/src/coalesce.c
+++ b/src/coalesce.c
@@ -74,7 +74,7 @@ SEXP coalesce(SEXP x, SEXP inplaceArg) {
     }
   } break;
   case REALSXP: {
-    if (INHERITS(first, char_integer64) || INHERITS(first, char_nanotime)) { // integer64 and nanotime (it seem nanotime does not inherit from integer64)
+    if (Rinherits(first, char_integer64)) { // Rinherits() is true for nanotime
       int64_t *xP=(int64_t *)REAL(first), finalVal=NA_INTEGER64;
       int k=0;
       for (int j=0; j<nval; ++j) {
diff --git a/src/fifelse.c b/src/fifelse.c
index d18b0bc637..f702f1c732 100644
--- a/src/fifelse.c
+++ b/src/fifelse.c
@@ -91,7 +91,7 @@ SEXP fifelseR(SEXP l, SEXP a, SEXP b, SEXP na) {
     double *restrict pans = REAL(ans);
     const double *restrict pa   = REAL(a);
     const double *restrict pb   = REAL(b);
-    const double na_double = (INHERITS(a, char_integer64) || INHERITS(a, char_nanotime)) ? NA_INT64_D : NA_REAL; // integer64 and nanotime support
+    const double na_double = Rinherits(a, char_integer64) ? NA_INT64_D : NA_REAL; // Rinherits() is true for nanotime
     const double pna = nonna ? REAL(na)[0] : na_double;
     #pragma omp parallel for num_threads(getDTthreads())
     for (int64_t i=0; i<len0; ++i) {
diff --git a/src/nafill.c b/src/nafill.c
index 74ac4f927f..59b9f2c8b5 100644
--- a/src/nafill.c
+++ b/src/nafill.c
@@ -134,7 +134,7 @@ SEXP nafillR(SEXP obj, SEXP type, SEXP fill, SEXP inplace, SEXP cols, SEXP verbo
     SEXP this_x = VECTOR_ELT(x, i);
     switch (TYPEOF(this_x)) {
     case REALSXP : {
-      if (INHERITS(this_x, char_integer64) || INHERITS(this_x, char_nanotime)) {
+      if (INHERITS(this_x, char_integer64) || INHERITS(this_x, char_nanotime)) {  // inside parallel region so can't call Rinherits()
         nafillInteger64(i64x[i], inx[i], itype, i64fill, &vans[i], bverbose);
       } else {
         nafillDouble(dx[i], inx[i], itype, dfill, &vans[i], bverbose);
diff --git a/src/utils.c b/src/utils.c
index c6b0dc52c7..ce4cfc1d4e 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -98,7 +98,7 @@ void coerceFill(SEXP fill, double *dfill, int32_t *ifill, int64_t *i64fill) {
       i64fill[0] = (int64_t)(INTEGER(fill)[0]);
     }
   } else if (isReal(fill)) {
-    if (INHERITS(fill,char_integer64) || INHERITS(fill,char_nanotime)) {
+    if (Rinherits(fill,char_integer64)) {  // Rinherits true for nanotime
       long long *llfill = (long long *)REAL(fill);
       if (llfill[0]==NA_INT64_LL) {
         ifill[0] = NA_INTEGER; dfill[0] = NA_REAL; i64fill[0] = NA_INTEGER64;