diff --git a/src/rinterface.h b/src/rinterface.h
index 3a164ee9da..dada9a184b 100644
--- a/src/rinterface.h
+++ b/src/rinterface.h
@@ -108,6 +108,9 @@ igraph_error_t R_SEXP_to_igraph_eigen_which(SEXP in, igraph_eigen_which_t *out);
 void           R_SEXP_to_igraph_arpack_options(SEXP in, igraph_arpack_options_t *opt);
 igraph_error_t R_SEXP_to_attr_comb(SEXP input, igraph_attribute_combination_t *comb);
 
+/* The following IGRAPH_R_... macros must only be called from top-level C code,
+ * i.e. in C functions which are called from R directly. */
+
 #define IGRAPH_R_CHECK(func) \
     do { \
         R_igraph_attribute_clean_preserve_list(); \
diff --git a/src/rinterface_extra.c b/src/rinterface_extra.c
index 9a529966b0..ed58f22132 100644
--- a/src/rinterface_extra.c
+++ b/src/rinterface_extra.c
@@ -67,6 +67,9 @@ enum igraph_versions {
 
 #define R_IGRAPH_VERSION_VAR ".__igraph_version__."
 
+/* The following three R_check_... functions must only be called from top-level C code,
+ * i.e. in contexts where igraph_error() does NOT return. */
+
 void R_check_int_scalar(SEXP value)
 {
   if (Rf_xlength(value) != 1) {