diff --git a/doc/source/reference/language/builtin_functions.rst b/doc/source/reference/language/builtin_functions.rst
index 1da388f..aeaa42f 100644
--- a/doc/source/reference/language/builtin_functions.rst
+++ b/doc/source/reference/language/builtin_functions.rst
@@ -53,9 +53,9 @@ returns the const table of the VM.
 
 sets the const table of the VM; returns the previous const table.
 
-.. js:function:: assert(exp)
+.. js:function:: assert(exp, [message])
 
-throws an exception if exp is null
+throws an exception if exp is null or false. Throws "assertion failed" string by default, or message if specified.
 
 .. js:function:: print(x)
 
diff --git a/squirrel/sqbaselib.cpp b/squirrel/sqbaselib.cpp
index 5c74693..b37c975 100644
--- a/squirrel/sqbaselib.cpp
+++ b/squirrel/sqbaselib.cpp
@@ -156,7 +156,14 @@ static SQInteger base_getstackinfos(HSQUIRRELVM v)
 static SQInteger base_assert(HSQUIRRELVM v)
 {
     if(SQVM::IsFalse(stack_get(v,2))){
-        return sq_throwerror(v,_SC("assertion failed"));
+        SQInteger top = sq_gettop(v);
+        if (top>2 && SQ_SUCCEEDED(sq_tostring(v,3))) {
+            const SQChar *str = 0;
+            if (SQ_SUCCEEDED(sq_getstring(v,-1,&str))) {
+                return sq_throwerror(v, str);
+            }
+        }
+        return sq_throwerror(v, _SC("assertion failed"));
     }
     return 0;
 }
@@ -283,7 +290,7 @@ static const SQRegFunction base_funcs[]={
     {_SC("setroottable"),base_setroottable,2, NULL},
     {_SC("getconsttable"),base_getconsttable,1, NULL},
     {_SC("setconsttable"),base_setconsttable,2, NULL},
-    {_SC("assert"),base_assert,2, NULL},
+    {_SC("assert"),base_assert,-2, NULL},
     {_SC("print"),base_print,2, NULL},
     {_SC("error"),base_error,2, NULL},
     {_SC("compilestring"),base_compilestring,-2, _SC(".ss")},