diff --git a/Radio.cpp b/Radio.cpp
index e5b34c35d..56b943739 100644
--- a/Radio.cpp
+++ b/Radio.cpp
@@ -14,10 +14,16 @@ namespace Radio
     double constexpr MHz_factor {1.e6};
     int constexpr frequency_precsion {6};
 
+    // valid callsign alphabet
+    QRegularExpression callsign_alphabet_re {R"(^[A-Z0-9/]{3,11}$)"};
+
     // very loose validation - callsign must contain a letter next to
     // a number
     QRegularExpression valid_callsign_regexp {R"(\d[[:alpha:]]|[[:alpha:]]\d)"};
 
+    // standard callsign
+    QRegularExpression strict_standard_callsign_re {R"(^([A-Z][0-9]?|[0-9][A-Z])[0-9][A-Z]{0,3}$)"};
+
     // suffixes that are often used and should not be interpreted as a
     // DXCC Entity prefix used as a suffix
     QRegularExpression non_prefix_suffix {R"(\A([0-9AMPQR]|QRP|F[DF]|[AM]M|L[HT]|LGT)\z)"};
@@ -112,6 +118,12 @@ namespace Radio
     return callsign.contains ('/');
   }
 
+  bool is_77bit_nonstandard_callsign (QString const& callsign)
+  {
+    return callsign.contains (callsign_alphabet_re)
+      && !callsign.contains (strict_standard_callsign_re);
+  }
+
   // split on first '/' and return the larger portion or the whole if
   // there is no '/'
   QString base_callsign (QString callsign)
diff --git a/Radio.hpp b/Radio.hpp
index e63abf4b8..4cc549b8b 100644
--- a/Radio.hpp
+++ b/Radio.hpp
@@ -53,6 +53,7 @@ namespace Radio
   //
   bool UDP_EXPORT is_callsign (QString const&);
   bool UDP_EXPORT is_compound_callsign (QString const&);
+  bool is_77bit_nonstandard_callsign (QString const&);
   QString UDP_EXPORT base_callsign (QString);
   QString UDP_EXPORT effective_prefix (QString);
 }