diff --git a/bibcop.pl b/bibcop.pl
index 2020e05..816c1d9 100755
--- a/bibcop.pl
+++ b/bibcop.pl
@@ -755,7 +755,7 @@ sub listed_tags {
 # Make sure the text can safely be rendered in TeX.
 sub escape_tex {
   my ($tex) = @_;
-  $tex =~ s/[^a-zA-Z0-9-.+)(:; ]/?/g;
+  $tex =~ s/[^a-zA-Z0-9-.,+)(:; '"]/?/g;
   return $tex;
 }
 
diff --git a/testfiles/bibtex.luatex.tlg b/testfiles/bibtex.luatex.tlg
index 0024407..f644fc5 100644
--- a/testfiles/bibtex.luatex.tlg
+++ b/testfiles/bibtex.luatex.tlg
@@ -4,9 +4,9 @@ LaTeX Warning: Citation `dijkstra1968letters' on page 1 undefined on input line
 runsystem((perl ./bibcop.pl --verbose       --latex 'main.bib') > iexec.tmp 2>&1; /bin/echo -n $?% >iexec.ret)...executed
 (iexec.tmp bibcop: 1 entries found in main.bib
 bibcop: Checking dijkstra1968letters (no.0)...
-Package bibcop Warning: All minor words in the ?title? must be lower-cased? while the 6th word ?To? is not? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: A mandatory ?doi? tag for ??article? is missing among (author? journal? number? pages? publisher? title? volume? year)? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: The ?title? must be wrapped in double curled brackets? in the ?dijkstra1968letters? entry.
+Package bibcop Warning: All minor words in the 'title' must be lower-cased? while the 6th word 'To' is not? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: A mandatory 'doi' tag for '?article' is missing among (author? journal? number? pages? publisher? title? volume? year)? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: The 'title' must be wrapped in double curled brackets? in the 'dijkstra1968letters' entry.
 bibcop: 3 problem(s) found
 ) iexec: The content of 'iexec.tmp' was included into the document
 runsystem(rm iexec.tmp)...executed
diff --git a/testfiles/bibtex.tlg b/testfiles/bibtex.tlg
index 05076be..54b9c0f 100644
--- a/testfiles/bibtex.tlg
+++ b/testfiles/bibtex.tlg
@@ -4,9 +4,9 @@ LaTeX Warning: Citation `dijkstra1968letters' on page 1 undefined on input line
 runsystem((perl ./bibcop.pl --verbose       --latex 'main.bib') > iexec.tmp 2>&1; /bin/echo -n $?% >iexec.ret)...executed.
 (iexec.tmp bibcop: 1 entries found in main.bib
 bibcop: Checking dijkstra1968letters (no.0)...
-Package bibcop Warning: All minor words in the ?title? must be lower-cased? while the 6th word ?To? is not? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: A mandatory ?doi? tag for ??article? is missing among (author? journal? number? pages? publisher? title? volume? year)? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: The ?title? must be wrapped in double curled brackets? in the ?dijkstra1968letters? entry.
+Package bibcop Warning: All minor words in the 'title' must be lower-cased? while the 6th word 'To' is not? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: A mandatory 'doi' tag for '?article' is missing among (author? journal? number? pages? publisher? title? volume? year)? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: The 'title' must be wrapped in double curled brackets? in the 'dijkstra1968letters' entry.
 bibcop: 3 problem(s) found
 ) iexec: The content of 'iexec.tmp' was included into the document
 runsystem(rm iexec.tmp)...executed.
diff --git a/testfiles/bibtex.xetex.tlg b/testfiles/bibtex.xetex.tlg
index 05076be..54b9c0f 100644
--- a/testfiles/bibtex.xetex.tlg
+++ b/testfiles/bibtex.xetex.tlg
@@ -4,9 +4,9 @@ LaTeX Warning: Citation `dijkstra1968letters' on page 1 undefined on input line
 runsystem((perl ./bibcop.pl --verbose       --latex 'main.bib') > iexec.tmp 2>&1; /bin/echo -n $?% >iexec.ret)...executed.
 (iexec.tmp bibcop: 1 entries found in main.bib
 bibcop: Checking dijkstra1968letters (no.0)...
-Package bibcop Warning: All minor words in the ?title? must be lower-cased? while the 6th word ?To? is not? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: A mandatory ?doi? tag for ??article? is missing among (author? journal? number? pages? publisher? title? volume? year)? in the ?dijkstra1968letters? entry.
-Package bibcop Warning: The ?title? must be wrapped in double curled brackets? in the ?dijkstra1968letters? entry.
+Package bibcop Warning: All minor words in the 'title' must be lower-cased? while the 6th word 'To' is not? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: A mandatory 'doi' tag for '?article' is missing among (author? journal? number? pages? publisher? title? volume? year)? in the 'dijkstra1968letters' entry.
+Package bibcop Warning: The 'title' must be wrapped in double curled brackets? in the 'dijkstra1968letters' entry.
 bibcop: 3 problem(s) found
 ) iexec: The content of 'iexec.tmp' was included into the document
 runsystem(rm iexec.tmp)...executed.