diff --git a/crawl.py b/crawl.py
index 4d1c6d7..18a9877 100755
--- a/crawl.py
+++ b/crawl.py
@@ -79,20 +79,24 @@ def _process_stdin(argv: str, res: utils.CurrencyResult) -> None:
             sys.exit()
         elif argv[0] in ['date', 'd']:
             print(res.date)
-        elif is_float(argv[0]):
-            # amount first -> convert to currency in argv[1] 
-            print(fmt_and_calc(
-                cur=argv[1].upper(),
-                amt=float(argv[0]),
-                res=res,
-                direction=DIRECTION_FROM_EUR))
-        elif is_float(argv[1]):
-            # currency first -> convert to EUR 
-            print(fmt_and_calc(
-                cur=argv[0].upper(),
-                amt=float(argv[1]),
-                res=res,
-                direction=DIRECTION_TO_EUR))
+        elif len(argv[0])==3 or len(argv[1])==3:
+            # more than 3 letter abbreviations are invalid
+            if is_float(argv[0]):
+                # amount first -> convert to currency in argv[1] 
+                print(fmt_and_calc(
+                    cur=argv[1].upper(),
+                    amt=float(argv[0]),
+                    res=res,
+                    direction=DIRECTION_FROM_EUR))
+            elif is_float(argv[1]):
+                # currency first -> convert to EUR 
+                print(fmt_and_calc(
+                    cur=argv[0].upper(),
+                    amt=float(argv[1]),
+                    res=res,
+                    direction=DIRECTION_TO_EUR))
+        else:
+            print("Not implemented: '" + " ".join(argv) + "'")
     except IndexError:
         if argv is None:
             pass