diff --git a/rir/src/api.cpp b/rir/src/api.cpp
index 22570da6d..487dce219 100644
--- a/rir/src/api.cpp
+++ b/rir/src/api.cpp
@@ -601,10 +601,7 @@ REXPORT SEXP rirCreateSimpleIntContext() {
     return res;
 }
 
-REXPORT SEXP playground() {
-
-    return R_NilValue;
-}
+REXPORT SEXP playground() { return R_NilValue; }
 
 bool startup() {
     initializeRuntime();
diff --git a/rir/src/compiler/native/builtins.cpp b/rir/src/compiler/native/builtins.cpp
index bd3f627c9..74513b669 100644
--- a/rir/src/compiler/native/builtins.cpp
+++ b/rir/src/compiler/native/builtins.cpp
@@ -2247,7 +2247,7 @@ bool deoptChaosTriggerImpl(bool deoptTrue) {
 void checkTypeImpl(SEXP val, uint64_t type, const char* msg) {
     assert(pir::Parameter::RIR_CHECK_PIR_TYPES);
     pir::PirType typ(type);
-    if (!typ.isInstance(val)) {
+    if (!typ.isInstance(val, true)) {
         std::cerr << "type assert failed\n";
         std::cerr << "got " << pir::PirType(val) << " but expected a " << typ
                   << ":\n";
diff --git a/rir/src/compiler/pir/instruction.cpp b/rir/src/compiler/pir/instruction.cpp
index e18e28c05..42947010d 100644
--- a/rir/src/compiler/pir/instruction.cpp
+++ b/rir/src/compiler/pir/instruction.cpp
@@ -877,6 +877,19 @@ PirType CallSafeBuiltin::inferType(const Instruction::GetType& getType) const {
         inferred = PirType(RType::vec).orAttribsOrObj();
     }
 
+    if ("dim" == name) {
+        if (!getType(callArg(0).val())
+                 .maybeObj()) { // TODO: is it necessary to check this?
+            // inferred = (PirType(RType::integer) | RType::nil)
+            //                .notMissing()
+            //                .orAttribsOrObj();
+
+            // if (!getType(callArg(0).val()).maybeHasAttrs()) {
+            //     inferred = PirType(RType::nil);
+            // }
+        }
+    }
+
     if (inferred != PirType::bottom())
         return inferred & type;
 
diff --git a/rir/src/compiler/pir/type.cpp b/rir/src/compiler/pir/type.cpp
index a5a8b19ee..8d6c0aea3 100644
--- a/rir/src/compiler/pir/type.cpp
+++ b/rir/src/compiler/pir/type.cpp
@@ -95,14 +95,17 @@ void PirType::merge(SEXPTYPE sexptype) {
 // contain NaN for the benefit, so we simple assume they do
 static const R_xlen_t MAX_SIZE_OF_VECTOR_FOR_NAN_CHECK = 1;
 
-static bool maybeContainsNAOrNaN(SEXP vector) {
+static bool maybeContainsNAOrNaN(SEXP vector, bool exact) {
     if (TYPEOF(vector) == CHARSXP) {
         return vector == NA_STRING;
     } else if (TYPEOF(vector) == INTSXP || TYPEOF(vector) == REALSXP ||
                TYPEOF(vector) == LGLSXP || TYPEOF(vector) == CPLXSXP ||
                TYPEOF(vector) == STRSXP) {
-        if (XLENGTH(vector) > MAX_SIZE_OF_VECTOR_FOR_NAN_CHECK) {
-            return true;
+
+        if (!exact) {
+            if (XLENGTH(vector) > MAX_SIZE_OF_VECTOR_FOR_NAN_CHECK) {
+                return true;
+            }
         }
         for (int i = 0; i < XLENGTH(vector); i++) {
             switch (TYPEOF(vector)) {
@@ -137,7 +140,7 @@ static bool maybeContainsNAOrNaN(SEXP vector) {
     }
 }
 
-PirType::PirType(SEXP e) : flags_(topRTypeFlags()), t_(RTypeSet()) {
+PirType::PirType(SEXP e, bool exact) : flags_(topRTypeFlags()), t_(RTypeSet()) {
 
     if (e == R_MissingArg) {
         *this = theMissingValue();
@@ -179,7 +182,7 @@ PirType::PirType(SEXP e) : flags_(topRTypeFlags()), t_(RTypeSet()) {
     if (t != LISTSXP && t != EXTERNALSXP && t != BCODESXP && t != LANGSXP)
         if (Rf_xlength(e) == 1)
             flags_.reset(TypeFlags::maybeNotScalar);
-    if (!maybeContainsNAOrNaN(e))
+    if (!maybeContainsNAOrNaN(e, exact))
         flags_.reset(TypeFlags::maybeNAOrNaN);
 }
 
@@ -210,14 +213,14 @@ void PirType::merge(const ObservedValues& other) {
         *this = orSexpTypes(any());
 }
 
-bool PirType::isInstance(SEXP val) const {
+bool PirType::isInstance(SEXP val, bool exact) const {
     if (isRType()) {
         if (TYPEOF(val) == PROMSXP) {
             assert(!Rf_isObject(val));
             if (maybePromiseWrapped() && !maybeLazy()) {
                 auto v = PRVALUE(val);
                 return v != R_UnboundValue &&
-                       notMissing().forced().isInstance(v);
+                       notMissing().forced().isInstance(v, exact);
             }
             return maybe(RType::prom) || (maybeLazy() && maybePromiseWrapped());
         }
@@ -229,7 +232,9 @@ bool PirType::isInstance(SEXP val) const {
             return IS_SIMPLE_SCALAR(val, LGLSXP) &&
                    LOGICAL(val)[0] != NA_LOGICAL;
         }
-        return PirType(val).isA(*this);
+
+        return PirType(val, exact).isA(*this);
+        ;
     } else {
         std::cerr << "can't check val is instance of " << *this << ", value:\n";
         Rf_PrintValue(val);
diff --git a/rir/src/compiler/pir/type.h b/rir/src/compiler/pir/type.h
index 5202344ff..26ffe1888 100644
--- a/rir/src/compiler/pir/type.h
+++ b/rir/src/compiler/pir/type.h
@@ -179,7 +179,7 @@ struct PirType {
     // cppcheck-suppress noExplicitConstructor
     constexpr PirType(const NativeTypeSet& t) : t_(t) {}
 
-    explicit PirType(SEXP);
+    explicit PirType(SEXP, bool exact = false);
     constexpr PirType(const PirType& other)
         : flags_(other.flags_), t_(other.t_) {}
 
@@ -641,7 +641,8 @@ struct PirType {
             // NULL
             return RType::nil;
         }
-        if (isA((num() | RType::str | RType::list | RType::code)
+        if (isA((num() | RType::str | RType::list |
+                 RType::code /* | RType::nil  */)
                     .orAttribsOrObj())) {
             // If the index is out of bounds, NA is returned (even if both args
             // are non-NA) so we must add orNAOrNaN()
@@ -750,7 +751,7 @@ struct PirType {
     }
 
     // Is val an instance of this type?
-    bool isInstance(SEXP val) const;
+    bool isInstance(SEXP val, bool exact = false) const;
 
     void print(std::ostream& out = std::cout) const;
 
diff --git a/rir/src/compiler/pir/value.cpp b/rir/src/compiler/pir/value.cpp
index bd9380e56..19513c97e 100644
--- a/rir/src/compiler/pir/value.cpp
+++ b/rir/src/compiler/pir/value.cpp
@@ -56,6 +56,7 @@ void Value::callArgTypeToContext(Context& assumptions, unsigned i) const {
     arg = arg->cFollowCastsAndForce();
     if (!MkArg::Cast(arg))
         check(arg);
+
 }
 
 void Value::checkReplace(Value* replace) const {