diff --git a/doc/c64.sgml b/doc/c64.sgml
index 5aac45af2..1ebcab31f 100644
--- a/doc/c64.sgml
+++ b/doc/c64.sgml
@@ -269,6 +269,16 @@ The program return code (low byte) is passed back to BASIC by use of the
 <tt/ST/ variable.
 
 
+<sect1>Interrupts<p>
+
+The runtime for the C64 uses routines marked as <tt/.CONDES/ type 2 for
+interrupt handlers. Such routines must be written as simple machine language
+subroutines and will be called automatically by the interrupt handler code
+when they are linked into a program. See the discussion of the <tt/.CONDES/
+feature in the <htmlurl url="ca65.html" name="assembler manual">.
+                       
+
+
 <sect>Bugs/Feedback<p>
 
 If you have problems using the library, if you find any bugs, or if you're