diff --git a/git-latexdiff b/git-latexdiff
index 4df062b..69422d4 100755
--- a/git-latexdiff
+++ b/git-latexdiff
@@ -78,6 +78,7 @@ Options:
                                   deleted.
 
     --latexmk             use latexmk
+    --latexopt            pass additional options to latex (e.g. -shell-escape)
     -o <file>, --output <file>
                           copy resulting PDF into <file> (usually ending with .pdf)
                           Implies "--cleanup all"
@@ -136,6 +137,7 @@ tmpdir_prefix="/tmp"
 prepare_cmd=
 subtree=0
 uselatexmk=
+latexopt=
 ln_untracked=0
 quiet=0
 
@@ -209,6 +211,10 @@ while test $# -ne 0; do
         "--latexmk")
             uselatexmk=1
             ;;
+	"--latexopt")
+	    shift
+	    latexopt=$1
+	    ;;
         "--ln-untracked")
             ln_untracked=1
             ;;
@@ -299,12 +305,6 @@ if test -z "$main" ; then
     main=$(git grep -l '^[ \t]*\\documentclass')
     # May return multiple results, but if so the result won't be a file.
     if test -r "$main" ; then
-	ext=${main##*\.}
-        case "$ext" in
-	    Rnw) check_knitr ;;
-	    Rtex) check_knitr ;;
-	    *) ;;
-	esac
 	echo "Using $main as the main file."
     else
 	if test -z "$main" ; then
@@ -317,6 +317,13 @@ if test -z "$main" ; then
     fi
 fi
 
+ext=${main##*\.}
+case "$ext" in
+    Rnw) check_knitr ;;
+    Rtex) check_knitr ;;
+    *) ;;
+esac
+
 if test ! -r "$main" ; then
     die "Cannot read $main."
 fi
@@ -401,9 +408,9 @@ elif test "$uselatexmk" = 1; then
     log_cmd latexmk.log latexmk -f -pdf -silent "$mainbase" || compile_error=1
 else
     if [ "$quiet" = 1 ]; then
-	latexopt="-interaction=nonstopmode"
+	latexopt="$latexopt -interaction=nonstopmode"
     else
-	latexopt="-interaction=errorstopmode"
+	latexopt="$latexopt -interaction=errorstopmode"
     fi
     log_cmd pdflatex1.log pdflatex $latexopt "$mainbase" || compile_error=1
     if test "$bibtex" = 1 ; then