diff --git a/src/lib/png.c b/src/lib/png.c
index 7521d0965..3d167cd40 100644
--- a/src/lib/png.c
+++ b/src/lib/png.c
@@ -120,21 +120,28 @@ mmap_round_size(size_t s){
 
 // write a PNG, creating the buffer ourselves. it must be munmapped. the
 // resulting length is written to *bsize on success. returns MMAP_FAILED
-// on a failure. if |fname| is NULL, an anonymous map will be made.
-void* create_png_mmap(const ncvisual* ncv, size_t* bsize, const char* fname){
+// on a failure. if |fd| is negative, an anonymous map will be made.
+void* create_png_mmap(const ncvisual* ncv, size_t* bsize, int fd){
   const unsigned alphap = 1; // FIXME 0 if no alpha used, for smaller output
   *bsize = compute_png_size(ncv, alphap);
   *bsize = mmap_round_size(*bsize);
   if(*bsize == 0){
     return MAP_FAILED;
   }
-  // FIXME open and ftruncate file if fname is set
+  if(fd >= 0){
+    if(ftruncate(fd, *bsize) < 0){
+      logerror("Couldn't set size of %d to %zuB (%s)\n",
+               fd, *bsize, strerror(errno));
+      return MAP_FAILED;
+    }
+    loginfo("Set size of %d to %zuB\n", fd, *bsize);
+  }
   // FIXME hugetlb?
   void* map = mmap(NULL, *bsize, PROT_WRITE | PROT_READ,
                    MAP_SHARED_VALIDATE |
-                   (fname ? 0 : MAP_ANONYMOUS), -1, 0);
+                   (fd >= 0 ? 0 : MAP_ANONYMOUS), fd, 0);
   if(map == MAP_FAILED){
-    logerror("Couldn't get %zuB map\n", *bsize);
+    logerror("Couldn't get %zuB map for %d\n", *bsize, fd);
     return MAP_FAILED;
   }
   if(create_png(ncv, map, bsize, alphap)){
diff --git a/src/lib/png.h b/src/lib/png.h
new file mode 100644
index 000000000..e7217d67d
--- /dev/null
+++ b/src/lib/png.h
@@ -0,0 +1,18 @@
+#ifndef NOTCURSES_PNG
+#define NOTCURSES_PNG
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <sys/mman.h>
+
+struct ncvisual;
+
+void* create_png_mmap(const struct ncvisual* ncv, size_t* bsize, int fd);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/src/tests/png.cpp b/src/tests/png.cpp
deleted file mode 100644
index a1c313d4d..000000000
--- a/src/tests/png.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#include "main.h"
-#include "png.h"
-#include "visual-details.h"
-#include <vector>
-#include <cmath>
-
-TEST_CASE("PNG") {
-  auto nc_ = testing_notcurses();
-  REQUIRE(nullptr != nc_);
-  ncplane* ncp_ = notcurses_stdplane(nc_);
-  REQUIRE(ncp_);
-  auto n_ = notcurses_stdplane(nc_);
-  REQUIRE(n_);
-
-#ifndef NOTCURSES_USE_MULTIMEDIA
-#else
-  // write a 10x10 opaque PNG out, and ensure we can read it back
-  SUBCASE("ReadWrittenOpaquePNG") {
-    std::array<uint32_t, 100> pixels;
-    pixels.fill(htole(0x00ff0000ull)); // green, opaque set later
-    auto ncv = ncvisual_from_rgb_loose(pixels.data(), 10, 40, 10, 0xff);
-    REQUIRE(nullptr != ncv);
-    // FIXME write out ncvisual to PNG, read it back, render it
-    CHECK(0 == notcurses_render(nc_));
-    ncvisual_destroy(ncv);
-  }
-#endif
-
-  CHECK(!notcurses_stop(nc_));
-}