diff --git a/Lib/System/IdCTypes.pas b/Lib/System/IdCTypes.pas
index 5d8623c9d..906df7d07 100644
--- a/Lib/System/IdCTypes.pas
+++ b/Lib/System/IdCTypes.pas
@@ -296,6 +296,16 @@   TIdC_TM = record
     tm_wday: TIdC_INT;        (* day of the week, range 0 to 6    *)
     tm_yday: TIdC_INT;        (* day in the year, range 0 to 365  *)
     tm_isdst: TIdC_INT;       (* daylight saving time             *)
+    {$IFDEF LINUX}
+    // xjikka 20260112 glibc struct tm extension:
+    // ASN1_TIME_to_tm() writes a full glibc struct tm (tm_gmtoff, tm_zone).
+    // Without these fields TIdC_TM is too small, causing stack corruption
+    // (e.g. invalid X509 ValidFrom/ValidTo values) on Linux targets.
+    // This is especially visible with FPC cross-compilation to Linux/ARM
+    // (e.g. Raspberry Pi), where X509 ValidFrom/ValidTo values become invalid.
+    tm_gmtoff: TIdC_LONG;  // seconds east of UTC
+    tm_zone: PAnsiChar;    // timezone abbreviation
+    {$ENDIF}
   end;
   PIdC_TM = ^TIdC_TM;
   PPIdC_TM = ^PIdC_TM;
@@ -303,3 +313,5 @@   TIdC_TM = record
 implementation
 
 end.
+
+