diff --git a/dlls/jscript/jscript_En.rc b/dlls/jscript/jscript_En.rc
index 40b64c9ddaf..8a0a9a9cad5 100644
--- a/dlls/jscript/jscript_En.rc
+++ b/dlls/jscript/jscript_En.rc
@@ -22,9 +22,11 @@ LANGUAGE LANG_ENGLISH, SUBLANG_DEFAULT
 
 STRINGTABLE DISCARDABLE
 {
+    IDS_INVALID_CALL_ARG    "Invalid procedure call or argument"
     IDS_NO_PROPERTY         "Object doesn't support this property or method"
     IDS_ARG_NOT_OPT         "Argument not optional"
     IDS_NOT_DATE            "'[object]' is not a date object"
+    IDS_NOT_NUM             "Number expected"
     IDS_NOT_BOOL            "Boolean object expected"
     IDS_INVALID_LENGTH      "Array length must be a finite positive integer"
 }
diff --git a/dlls/jscript/number.c b/dlls/jscript/number.c
index 5399c91615a..28049a9270a 100644
--- a/dlls/jscript/number.c
+++ b/dlls/jscript/number.c
@@ -54,10 +54,8 @@ static HRESULT Number_toString(DispatchEx *dispex, LCID lcid, WORD flags, DISPPA
 
     TRACE("\n");
 
-    if(!is_class(dispex, JSCLASS_NUMBER)) {
-        FIXME("throw TypeError\n");
-        return E_FAIL;
-    }
+    if(!is_class(dispex, JSCLASS_NUMBER))
+        return throw_type_error(dispex->ctx, ei, IDS_NOT_NUM, NULL);
 
     number = (NumberInstance*)dispex;
 
@@ -66,10 +64,8 @@ static HRESULT Number_toString(DispatchEx *dispex, LCID lcid, WORD flags, DISPPA
         if(FAILED(hres))
             return hres;
 
-        if(radix<2 || radix>36) {
-            FIXME("throw TypeError\n");
-            return E_FAIL;
-        }
+        if(radix<2 || radix>36)
+            return throw_type_error(dispex->ctx, ei, IDS_INVALID_CALL_ARG, NULL);
     }
 
     if(V_VT(&number->num) == VT_I4)
@@ -208,10 +204,8 @@ static HRESULT Number_valueOf(DispatchEx *dispex, LCID lcid, WORD flags, DISPPAR
 {
     TRACE("\n");
 
-    if(!is_class(dispex, JSCLASS_NUMBER)) {
-        FIXME("throw TypeError\n");
-        return E_FAIL;
-    }
+    if(!is_class(dispex, JSCLASS_NUMBER))
+        return throw_type_error(dispex->ctx, ei, IDS_NOT_NUM, NULL);
 
     if(retv) {
         NumberInstance *number = (NumberInstance*)dispex;
diff --git a/dlls/jscript/resource.h b/dlls/jscript/resource.h
index 44c04a86497..8caff6a9b94 100644
--- a/dlls/jscript/resource.h
+++ b/dlls/jscript/resource.h
@@ -18,8 +18,10 @@
 
 #include <windef.h>
 
+#define IDS_INVALID_CALL_ARG                0x0005
 #define IDS_NO_PROPERTY                     0x01B6
 #define IDS_ARG_NOT_OPT                     0x01c1
 #define IDS_NOT_DATE                        0x138E
+#define IDS_NOT_NUM                         0x1389
 #define IDS_NOT_BOOL                        0x1392
 #define IDS_INVALID_LENGTH                  0x13A5
diff --git a/dlls/jscript/tests/api.js b/dlls/jscript/tests/api.js
index d0e599583c1..4cf5bb6664d 100644
--- a/dlls/jscript/tests/api.js
+++ b/dlls/jscript/tests/api.js
@@ -1302,5 +1302,7 @@ exception_test(function() {Array(-3);}, "RangeError");
 exception_test(function() {arr.toString = Boolean.prototype.toString; arr.toString();}, "TypeError");
 exception_test(function() {date.setTime();}, "TypeError");
 exception_test(function() {arr.test();}, "TypeError");
+exception_test(function() {arr.toString = Number.prototype.toString; arr.toString();}, "TypeError");
+exception_test(function() {(new Number(3)).toString(1);}, "TypeError");
 
 reportSuccess();