diff --git a/src/compat.h b/src/compat.h
new file mode 100644
index 00000000..1704a752
--- /dev/null
+++ b/src/compat.h
@@ -0,0 +1,17 @@
+#ifndef S7_COMPAT_H
+#define S7_COMPAT_H
+
+#if (R_VERSION >= R_Version(4, 5, 0))
+static inline
+SEXP s7_get_var_in_frame(SEXP env, SEXP sym, SEXP ifnotfound) {
+  return R_getVarEx(sym, env, FALSE, ifnotfound);
+}
+#else
+static inline
+SEXP s7_get_var_in_frame(SEXP env, SEXP sym, SEXP ifnotfound) {
+  SEXP val = Rf_findVarInFrame(env, sym);
+  return val == R_UnboundValue ? ifnotfound : val;
+}
+#endif
+
+#endif
diff --git a/src/method-dispatch.c b/src/method-dispatch.c
index 3594319f..d0901685 100644
--- a/src/method-dispatch.c
+++ b/src/method-dispatch.c
@@ -2,6 +2,7 @@
 #include <R.h>
 #include <Rinternals.h>
 #include <Rversion.h>
+#include "compat.h"
 
 #if (R_VERSION >= R_Version(4, 5, 0))
 #define getClosureFormals R_ClosureFormals
@@ -58,7 +59,7 @@ SEXP method_rec(SEXP table, SEXP signature, R_xlen_t signature_itr) {
 
   for (R_xlen_t i = 0; i < Rf_xlength(classes); ++i) {
     SEXP klass = Rf_install(CHAR(STRING_ELT(classes, i)));
-    SEXP val = Rf_findVarInFrame(table, klass);
+    SEXP val = s7_get_var_in_frame(table, klass, R_NilValue);
     if (TYPEOF(val) == ENVSXP) {
       PROTECT(val); // no really necessary, but rchk flags spuriously
       val = method_rec(val, signature, signature_itr + 1);
@@ -70,7 +71,7 @@ SEXP method_rec(SEXP table, SEXP signature, R_xlen_t signature_itr) {
   }
 
   // ANY fallback
-  SEXP val = Rf_findVarInFrame(table, sym_ANY);
+  SEXP val = s7_get_var_in_frame(table, sym_ANY, R_NilValue);
   if (TYPEOF(val) == ENVSXP) {
     PROTECT(val);
     val = method_rec(val, signature, signature_itr + 1);
diff --git a/src/prop.c b/src/prop.c
index 1086fa0d..c94eb3a4 100644
--- a/src/prop.c
+++ b/src/prop.c
@@ -1,6 +1,8 @@
 #define R_NO_REMAP
 #include <R.h>
 #include <Rinternals.h>
+#include <Rversion.h>
+#include "compat.h"
 
 extern SEXP sym_S7_class;
 
@@ -28,6 +30,14 @@ SEXP eval_here(SEXP lang) {
   return ans;
 }
 
+static inline
+SEXP ns_get(const char* name) {
+  SEXP val = s7_get_var_in_frame(ns_S7, Rf_install(name), R_UnboundValue);
+  if (val == R_UnboundValue)
+    Rf_error("Can't find `%s` in the S7 namespace", name);
+  return val;
+}
+
 static inline
 SEXP do_call1(SEXP fn, SEXP arg) {
   SEXP call, answer;
@@ -77,7 +87,7 @@ static __attribute__((noreturn))
 void signal_is_not_S7(SEXP object) {
   static SEXP check_is_S7 = NULL;
   if (check_is_S7 == NULL)
-    check_is_S7 = Rf_findVarInFrame(ns_S7, Rf_install("check_is_S7"));
+    check_is_S7 = ns_get("check_is_S7");
 
   // will signal error
   eval_here(Rf_lang2(check_is_S7, object));
@@ -89,7 +99,7 @@ static __attribute__((noreturn))
 void signal_prop_error(const char* fmt, SEXP object, SEXP name) {
   static SEXP signal_prop_error = NULL;
   if (signal_prop_error == NULL)
-    signal_prop_error = Rf_findVarInFrame(ns_S7, Rf_install("signal_prop_error"));
+    signal_prop_error = ns_get("signal_prop_error");
 
   eval_here(Rf_lang4(signal_prop_error, Rf_mkString(fmt), object, name));
   while(1);
@@ -109,7 +119,7 @@ void signal_error(SEXP errmsg) {
   // fallback to calling base::stop(errmsg)
   static SEXP signal_error = NULL;
   if (signal_error == NULL)
-    signal_error = Rf_findVarInFrame(ns_S7, Rf_install("signal_error"));
+    signal_error = ns_get("signal_error");
 
   eval_here(Rf_lang2(signal_error, errmsg));
   while(1);
@@ -242,7 +252,7 @@ void prop_validate(SEXP property, SEXP value, SEXP object) {
 
   static SEXP prop_validate = NULL;
   if (prop_validate == NULL)
-    prop_validate = Rf_findVarInFrame(ns_S7, Rf_install("prop_validate"));
+    prop_validate = ns_get("prop_validate");
 
   SEXP errmsg = eval_here(Rf_lang4(prop_validate, property, value, object));
   if (errmsg != R_NilValue) signal_error(errmsg);
@@ -252,7 +262,7 @@ static inline
 void obj_validate(SEXP object) {
   static SEXP validate = NULL;
   if (validate == NULL)
-    validate = Rf_findVarInFrame(ns_S7, Rf_install("validate"));
+    validate = ns_get("validate");
 
   switch (TYPEOF(object)) {
   case LANGSXP: