diff --git a/xpdf/xpdf/FlateStream.cc b/xpdf/xpdf/FlateStream.cc
index cfdd6fdd6..0e6b06e9b 100644
--- a/xpdf/xpdf/FlateStream.cc
+++ b/xpdf/xpdf/FlateStream.cc
@@ -89,7 +89,7 @@ int FlateStream::fill_buffer() {
   return 0;
 }
 
-GString *FlateStream::getPSFilter(int psLevel, char *indent) {
+GString *FlateStream::getPSFilter(int psLevel, const char *indent) {
   GString *s;
 
   if (psLevel < 3 || pred) {
diff --git a/xpdf/xpdf/FlateStream.h b/xpdf/xpdf/FlateStream.h
index 6f00b5b14..357f5714e 100644
--- a/xpdf/xpdf/FlateStream.h
+++ b/xpdf/xpdf/FlateStream.h
@@ -50,7 +50,7 @@ public:
   virtual int getChar();
   virtual int lookChar();
   virtual int getRawChar();
-  virtual GString *getPSFilter(int psLevel, char *indent);
+  virtual GString *getPSFilter(int psLevel, const char *indent);
   virtual GBool isBinary(GBool last = gTrue);
 
 private: