diff --git a/src/api/pdfrenderer.cpp b/src/api/pdfrenderer.cpp
index 0ddcd30609..9aacd3f74b 100644
--- a/src/api/pdfrenderer.cpp
+++ b/src/api/pdfrenderer.cpp
@@ -696,7 +696,7 @@ bool TessPDFRenderer::BeginDocumentHandler() {
 }
 
 bool TessPDFRenderer::imageToPDFObj(Pix *pix,
-                                    char *filename,
+                                    const char* filename,
                                     long int objnum,
                                     char **pdf_object,
                                     long int *pdf_object_size) {
@@ -845,7 +845,7 @@ bool TessPDFRenderer::AddImageHandler(TessBaseAPI* api) {
   char buf[kBasicBufSize];
   char buf2[kBasicBufSize];
   Pix *pix = api->GetInputImage();
-  char *filename = (char *)api->GetInputName();
+  const char* filename = reinterpret_cast<const char*>(api->GetInputName());
   int ppi = api->GetSourceYResolution();
   if (!pix || ppi <= 0)
     return false;
diff --git a/src/api/renderer.h b/src/api/renderer.h
index 0a72317620..bc773f85d7 100644
--- a/src/api/renderer.h
+++ b/src/api/renderer.h
@@ -212,8 +212,8 @@ class TESS_API TessPDFRenderer : public TessResultRenderer {
   // Create the /Contents object for an entire page.
   char* GetPDFTextObjects(TessBaseAPI* api, double width, double height);
   // Turn an image into a PDF object. Only transcode if we have to.
-  static bool imageToPDFObj(Pix *pix, char *filename, long int objnum,
-                          char **pdf_object, long int *pdf_object_size);
+  static bool imageToPDFObj(Pix* pix, const char* filename, long int objnum,
+                          char** pdf_object, long int* pdf_object_size);
 };