typo bf should be \bf
diff --git a/Doc/ext/ext.tex b/Doc/ext/ext.tex
index 7095bf8..4819124 100644
--- a/Doc/ext/ext.tex
+++ b/Doc/ext/ext.tex
@@ -1325,7 +1325,7 @@
 
 \subsection{SGI IRIX 4 Dynamic Loading}
 
-{bf IMPORTANT:} You must compile your extension module with the
+{\bf IMPORTANT:} You must compile your extension module with the
 additional C flag \samp{-G0} (or \samp{-G 0}).  This instruct the
 assembler to generate position-independent code.