diff --git a/lib.nas b/lib.nas
index 45f6bf5..a271acd 100644
--- a/lib.nas
+++ b/lib.nas
@@ -138,7 +138,9 @@ var math=
     exp:   func(x)  {return __builtin_exp(x);    }, 
     ln:    func(x)  {return __builtin_ln(x);     },
     sqrt:  func(x)  {return __builtin_sqrt(x);   },
-    atan2: func(x,y){return __builtin_atan2(x,y);}
+    atan2: func(x,y){return __builtin_atan2(x,y);},
+    nan:   func()   {return 1/0-1/0;             },
+    isnan: func(x)  {return __builtin_isnan(x);  }
 };
 
 var D2R=math.pi/180;
\ No newline at end of file
diff --git a/nasal.h b/nasal.h
index ad41a6c..1446dfd 100644
--- a/nasal.h
+++ b/nasal.h
@@ -15,7 +15,6 @@
 #include <cstdlib>
 #include <ctime>
 #include <cmath>
-#include <thread>
 #include <list>
 #include <stack>
 #include <queue>
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 9230eed..4b443b1 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -40,6 +40,7 @@ nasal_ref builtin_exp(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_ln(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_sqrt(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_atan2(std::vector<nasal_ref>&,nasal_gc&);
+nasal_ref builtin_isnan(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_time(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_contains(std::vector<nasal_ref>&,nasal_gc&);
 nasal_ref builtin_delete(std::vector<nasal_ref>&,nasal_gc&);
@@ -92,6 +93,7 @@ struct FUNC_TABLE
     {"__builtin_ln",      builtin_ln      },
     {"__builtin_sqrt",    builtin_sqrt    },
     {"__builtin_atan2",   builtin_atan2   },
+    {"__builtin_isnan",   builtin_isnan   },
     {"__builtin_time",    builtin_time    },
     {"__builtin_contains",builtin_contains},
     {"__builtin_delete",  builtin_delete  },
@@ -596,6 +598,13 @@ nasal_ref builtin_atan2(std::vector<nasal_ref>& local_scope,nasal_gc& gc)
     ret_addr->ptr.num=atan2(y_val_addr->ptr.num,x_val_addr->ptr.num);
     return ret_addr;
 }
+nasal_ref builtin_isnan(std::vector<nasal_ref>& local_scope,nasal_gc& gc)
+{
+    nasal_ref x=local_scope[1];
+    if(x->type==vm_num && std::isnan(x->ptr.num))
+        return gc.one_addr;
+    return gc.zero_addr;
+}
 nasal_ref builtin_time(std::vector<nasal_ref>& local_scope,nasal_gc& gc)
 {
     nasal_ref val_addr=local_scope[1];
diff --git a/stl/lib.nas b/stl/lib.nas
index 45f6bf5..a271acd 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -138,7 +138,9 @@ var math=
     exp:   func(x)  {return __builtin_exp(x);    }, 
     ln:    func(x)  {return __builtin_ln(x);     },
     sqrt:  func(x)  {return __builtin_sqrt(x);   },
-    atan2: func(x,y){return __builtin_atan2(x,y);}
+    atan2: func(x,y){return __builtin_atan2(x,y);},
+    nan:   func()   {return 1/0-1/0;             },
+    isnan: func(x)  {return __builtin_isnan(x);  }
 };
 
 var D2R=math.pi/180;
\ No newline at end of file
diff --git a/test/lexer.nas b/test/lexer.nas
index b66a9fa..737bd12 100644
--- a/test/lexer.nas
+++ b/test/lexer.nas
@@ -48,7 +48,7 @@ var lexer=func(file)
                     elsif(c=='r' ) str~='\r';
                     elsif(c=='t' ) str~='\t';
                     elsif(c=='v' ) str~='\v';
-                    elsif(c=='?' ) str~='?';
+                    elsif(c=='?' ) str~='\?';
                     elsif(c=='0' ) str~='\0';
                     elsif(c=='\\') str~='\\';
                     elsif(c=='\'') str~='\'';