diff --git a/src/user/user_mesh.cc b/src/user/user_mesh.cc
index a0abee9f..19029344 100644
--- a/src/user/user_mesh.cc
+++ b/src/user/user_mesh.cc
@@ -591,10 +591,10 @@ void mjCMesh::LoadOBJ(int default_provider) {
   mjResource* r = nullptr;
 
   // try reading from default provider
-  if((r = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
+  if ((r = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
     // try reading from filesystem
-    if (default_provider || (r = mju_openResource(filename.c_str(), 0)) == nullptr) {
-      throw mjCError(this, "could not parse OBJ file '%s'", filename.c_str());
+    if (!default_provider || (r = mju_openResource(filename.c_str(), 0)) == nullptr) {
+      throw mjCError(this, "could not open OBJ file '%s'", filename.c_str());
     }
   }
 
@@ -603,7 +603,7 @@ void mjCMesh::LoadOBJ(int default_provider) {
   int buffer_sz = mju_readResource(r, &bytes);
   if (buffer_sz < 0) {
     mju_closeResource(r);
-    throw mjCError(this, "could not parse OBJ file '%s'", filename.c_str());
+    throw mjCError(this, "could not read OBJ file '%s'", filename.c_str());
   }
 
   // TODO(etom): support .mtl files?
@@ -706,7 +706,7 @@ void mjCMesh::LoadSTL(int default_provider) {
   // still not found
   if (buffer_sz < 0) {
     mju_closeResource(r);
-    throw mjCError(this, "could not open STL file '%s'", filename.c_str());
+    throw mjCError(this, "could not read STL file '%s'", filename.c_str());
   } else if (!buffer_sz) {
     mju_closeResource(r);
     throw mjCError(this, "STL file '%s' is empty", filename.c_str());
@@ -792,7 +792,7 @@ void mjCMesh::LoadMSH(int default_provider) {
   if((r = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
     // fall back to OS filesystem
     if(!default_provider || (r = mju_openResource(filename.c_str(), 0)) == nullptr) {
-    throw mjCError(this, "could not open STL file '%s'", filename.c_str());
+    throw mjCError(this, "could not open MSH file '%s'", filename.c_str());
     }
   }
 
@@ -803,10 +803,10 @@ void mjCMesh::LoadMSH(int default_provider) {
   // still not found
   if (buffer_sz < 0) {
     mju_closeResource(r);
-    throw mjCError(this, "could not open STL file '%s'", filename.c_str());
+    throw mjCError(this, "could not read MSH file '%s'", filename.c_str());
   } else if (!buffer_sz) {
     mju_closeResource(r);
-    throw mjCError(this, "STL file '%s' is empty", filename.c_str());
+    throw mjCError(this, "MSH file '%s' is empty", filename.c_str());
   }
 
   // make sure header is present
@@ -1741,7 +1741,7 @@ void mjCSkin::LoadSKN(int default_provider) {
 
   if (buffer_sz < 0) {
     mju_closeResource(r);
-    throw mjCError(this, "could not open SKN file '%s'", filename.c_str());
+    throw mjCError(this, "could not read SKN file '%s'", filename.c_str());
   } else if (!buffer_sz) {
     mju_closeResource(r);
     throw mjCError(this, "SKN file '%s' is empty", filename.c_str());
diff --git a/src/user/user_objects.cc b/src/user/user_objects.cc
index d1bd7602..64f7dd5d 100644
--- a/src/user/user_objects.cc
+++ b/src/user/user_objects.cc
@@ -1983,7 +1983,7 @@ void mjCHField::LoadCustom(string filename, int default_provider) {
   const void* buffer = 0;
   mjResource* resource = nullptr;
 
-  if((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
+  if ((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
     // default to OS filesystem
     if (!default_provider || (resource = mju_openResource(filename.c_str(), 0)) == nullptr) {
       throw mjCError(this, "could not open hfield file '%s'", filename.c_str());
@@ -1994,7 +1994,7 @@ void mjCHField::LoadCustom(string filename, int default_provider) {
 
   // still not found
   if (!buffer || buffer_sz < 1) {
-    throw mjCError(this, "could not open hfield file '%s'", filename.c_str());
+    throw mjCError(this, "could not read hfield file '%s'", filename.c_str());
   }
 
   if (buffer_sz < 2*sizeof(int)) {
@@ -2041,8 +2041,11 @@ void mjCHField::LoadPNG(string filename, int default_provider) {
   const void* inbuffer = 0;
   mjResource* resource = nullptr;
 
-  if((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
-    throw mjCError(this, "could not open PNG file '%s'", filename.c_str());
+  if ((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
+    // try reading from filesystem
+    if (!default_provider || (resource = mju_openResource(filename.c_str(), 0)) == nullptr) {
+      throw mjCError(this, "could not open PNG file '%s' %d", filename.c_str(), default_provider);
+    }
   }
 
   int inbuffer_sz = mju_readResource(resource, &inbuffer);
@@ -2050,7 +2053,7 @@ void mjCHField::LoadPNG(string filename, int default_provider) {
   // still not found
   if (!inbuffer || inbuffer_sz < 1) {
     mju_closeResource(resource);
-    throw mjCError(this, "could not open PNG file '%s'", filename.c_str());
+    throw mjCError(this, "could not read PNG file '%s'", filename.c_str());
   }
 
   // load PNG from file or memory
@@ -2434,8 +2437,11 @@ void mjCTexture::LoadPNG(string filename, int default_provider,
   const void* inbuffer = 0;
   mjResource* resource = nullptr;
 
-  if((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
-    throw mjCError(this, "could not open PNG file '%s'", filename.c_str());
+  if ((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
+    // try reading from filesystem
+    if (!default_provider || (resource = mju_openResource(filename.c_str(), 0)) == nullptr) {
+      throw mjCError(this, "could not open PNG file '%s' %d", filename.c_str(), default_provider);
+    }
   }
 
   int inbuffer_sz = mju_readResource(resource, &inbuffer);
@@ -2443,7 +2449,7 @@ void mjCTexture::LoadPNG(string filename, int default_provider,
   // still not found
   if (!inbuffer || inbuffer_sz < 1) {
     mju_closeResource(resource);
-    throw mjCError(this, "could not open PNG file '%s'", filename.c_str());
+    throw mjCError(this, "could not read PNG file '%s'", filename.c_str());
   }
 
   // load PNG from file or memory
@@ -2469,7 +2475,7 @@ void mjCTexture::LoadCustom(string filename, int default_provider,
   const void* buffer = 0;
   mjResource* resource = nullptr;
 
-  if((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
+  if ((resource = mju_openResource(filename.c_str(), default_provider)) == nullptr) {
     // default to OS filesystem
     if (!default_provider || (resource = mju_openResource(filename.c_str(), 0)) == nullptr) {
       throw mjCError(this, "could not open texture file '%s'", filename.c_str());
@@ -2481,7 +2487,7 @@ void mjCTexture::LoadCustom(string filename, int default_provider,
   // still not found
   if (!buffer || buffer_sz < 0) {
     mju_closeResource(resource);
-    throw mjCError(this, "could not open texture file '%s'", filename.c_str());
+    throw mjCError(this, "could not read texture file '%s'", filename.c_str());
   }
 
   // read dimensions