diff --git a/src/common/datetime.cpp b/src/common/datetime.cpp
index c04f928cee..d95ea2093a 100644
--- a/src/common/datetime.cpp
+++ b/src/common/datetime.cpp
@@ -3429,6 +3429,19 @@ bool wxDateTime::IsWorkDay(Country WXUNUSED(country)) const
 // wxTimeSpan
 // ============================================================================
 
+// this enum is only used in wxTimeSpan::Format() below but we can't declare
+// it locally to the method as it provokes an internal compiler error in egcs
+// 2.91.60 when building with -O2
+enum TimeSpanPart
+{
+    Part_Week,
+    Part_Day,
+    Part_Hour,
+    Part_Min,
+    Part_Sec,
+    Part_MSec
+};
+
 // not all strftime(3) format specifiers make sense here because, for example,
 // a time span doesn't have a year nor a timezone
 //
@@ -3466,15 +3479,7 @@ wxString wxTimeSpan::Format(const wxChar *format) const
     // should use GetMinutes() % 60, otherwise just GetMinutes() &c
 
     // we remember the most important unit found so far
-    enum TimeSpanPart
-    {
-        Part_Week,
-        Part_Day,
-        Part_Hour,
-        Part_Min,
-        Part_Sec,
-        Part_MSec
-    } partBiggest = Part_MSec;
+    TimeSpanPart partBiggest = Part_MSec;
 
     for ( const wxChar *pch = format; *pch; pch++ )
     {