diff --git a/pkgs/development/interpreters/perl/builder.sh b/pkgs/development/interpreters/perl/builder.sh
index 09ffd1c16a84..14c1d3146b8d 100755
--- a/pkgs/development/interpreters/perl/builder.sh
+++ b/pkgs/development/interpreters/perl/builder.sh
@@ -8,21 +8,21 @@ cd perl-*
 
 # Perl's Configure messes with PATH.  We can't have that, so we patch it.
 # Yeah, this is an ugly hack.
-cat Configure | \
- grep -v '^paths=' | \
- grep -v '^locincpth=' | \
- grep -v '^xlibpth=' | \
- grep -v '^glibpth=' | \
- grep -v '^loclibpth=' | \
- grep -v '^locincpth=' | \
- cat > Configure.tmp
-mv Configure.tmp Configure
-chmod +x Configure
+if test "$NIX_ENFORCE_PURITY" = "1" -a -n "$NIX_STORE"; then
+    cat Configure | \
+        grep -v '^paths=' | \
+        grep -v '^locincpth=' | \
+        grep -v '^xlibpth=' | \
+        grep -v '^glibpth=' | \
+        grep -v '^loclibpth=' | \
+        grep -v '^locincpth=' | \
+        cat > Configure.tmp
+    mv Configure.tmp Configure
+    chmod +x Configure
+fi
 
 patch -p1 < $srcPatch
 
-./Configure -de -Dcc=gcc -Dprefix=$out -Uinstallusrbinperl \
- -Dlocincpth="$NIX_LIBC_INCLUDES" \
- -Dloclibpth="$NIX_LIBC_LIBS"
+./Configure -de -Dcc=gcc -Dprefix=$out -Uinstallusrbinperl
 make
 make install