diff --git a/CHANGES.md b/CHANGES.md
index ab8ad7c..68c11d0 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -8,6 +8,8 @@ v1.1.0 (Month DD, YYYY)
 - Added `pdfioFileCreateTemporary` function (Issue #29)
 - Added `pdfioDictIterateKeys` function (Issue #31)
 - Added `pdfioContentPathEnd` function.
+- Added protection against opening multiple streams in the same file at the
+  same time.
 - Fixed "install-shared" target (Issue #32)
 - Fixed `pdfioContentMatrixRotate` function.
 
diff --git a/pdfio-object.c b/pdfio-object.c
index d919982..6053518 100644
--- a/pdfio-object.c
+++ b/pdfio-object.c
@@ -1,7 +1,7 @@
 //
 // PDF object functions for PDFio.
 //
-// Copyright © 2021 by Michael R Sweet.
+// Copyright © 2021-2022 by Michael R Sweet.
 //
 // Licensed under Apache License v2.0.  See the file "LICENSE" for more
 // information.
@@ -33,8 +33,14 @@ pdfioObjClose(pdfio_obj_t *obj)		// I - Object
   if (!obj)
     return (false);
 
+  // Clear the current object pointer...
+  obj->pdf->current_obj = NULL;
+
   if (obj->pdf->mode != _PDFIO_MODE_WRITE)
-    return (true);			// Nothing to do when reading
+  {
+    // Nothing to do when reading
+    return (true);
+  }
 
   // Write what remains for the object...
   if (!obj->offset)
@@ -165,6 +171,12 @@ pdfioObjCreateStream(
     return (NULL);
   }
 
+  if (obj->pdf->current_obj)
+  {
+    _pdfioFileError(obj->pdf, "Another object (%u) is already open.", (unsigned)obj->pdf->current_obj->number);
+    return (NULL);
+  }
+
   // Write the header...
   if (!_pdfioDictGetValue(obj->value.value.dict, "Length"))
   {
@@ -193,7 +205,8 @@ pdfioObjCreateStream(
   if (!_pdfioFilePuts(obj->pdf, "stream\n"))
     return (NULL);
 
-  obj->stream_offset = _pdfioFileTell(obj->pdf);
+  obj->stream_offset    = _pdfioFileTell(obj->pdf);
+  obj->pdf->current_obj = obj;
 
   // Return the new stream...
   return (_pdfioStreamCreate(obj, length_obj, filter));
@@ -454,6 +467,12 @@ pdfioObjOpenStream(pdfio_obj_t *obj,	// I - Object
   if (!obj)
     return (NULL);
 
+  if (obj->pdf->current_obj)
+  {
+    _pdfioFileError(obj->pdf, "Another object (%u) is already open.", (unsigned)obj->pdf->current_obj->number);
+    return (NULL);
+  }
+
   // Make sure we've loaded the object dictionary...
   if (!obj->value.type)
   {
@@ -466,6 +485,8 @@ pdfioObjOpenStream(pdfio_obj_t *obj,	// I - Object
     return (NULL);
 
   // Open the stream...
+  obj->pdf->current_obj = obj;
+
   return (_pdfioStreamOpen(obj, decode));
 }
 
diff --git a/pdfio-private.h b/pdfio-private.h
index 9c59c75..cc6bf63 100644
--- a/pdfio-private.h
+++ b/pdfio-private.h
@@ -1,7 +1,7 @@
 //
 // Private header file for PDFio.
 //
-// Copyright © 2021 by Michael R Sweet.
+// Copyright © 2021-2022 by Michael R Sweet.
 //
 // Licensed under Apache License v2.0.  See the file "LICENSE" for more
 // information.
@@ -289,7 +289,8 @@ struct _pdfio_file_s			// PDF file structure
   pdfio_dict_t	**dicts;		// Dictionaries
   size_t	num_objs,		// Number of objects
 		alloc_objs;		// Allocated objects
-  pdfio_obj_t	**objs;			// Objects
+  pdfio_obj_t	**objs,			// Objects
+		*current_obj;		// Current object being written/read
   size_t	num_objmaps,		// Number of object maps
 		alloc_objmaps;		// Allocated object maps
   _pdfio_objmap_t *objmaps;		// Object maps
diff --git a/pdfio-stream.c b/pdfio-stream.c
index 7e35652..5fd54cc 100644
--- a/pdfio-stream.c
+++ b/pdfio-stream.c
@@ -174,6 +174,8 @@ pdfioStreamClose(pdfio_stream_t *st)	// I - Stream
 
   done:
 
+  st->pdf->current_obj = NULL;
+
   free(st->prbuffer);
   free(st->psbuffer);
   free(st);
diff --git a/testpdfio.c b/testpdfio.c
index d17c803..61f39c6 100644
--- a/testpdfio.c
+++ b/testpdfio.c
@@ -3239,13 +3239,13 @@ write_unit_file(
   // Create some image objects...
   fputs("pdfioFileCreateImageObjFromFile(\"testfiles/color.jpg\"): ", stdout);
   if ((color_jpg = pdfioFileCreateImageObjFromFile(outpdf, "testfiles/color.jpg", true)) != NULL)
-    puts("PASS");
+    printf("PASS (%u)\n", (unsigned)pdfioObjGetNumber(color_jpg));
   else
     return (1);
 
   fputs("pdfioFileCreateImageObjFromFile(\"testfiles/gray.jpg\"): ", stdout);
   if ((gray_jpg = pdfioFileCreateImageObjFromFile(outpdf, "testfiles/gray.jpg", true)) != NULL)
-    puts("PASS");
+    printf("PASS (%u)\n", (unsigned)pdfioObjGetNumber(gray_jpg));
   else
     return (1);