diff --git a/octoprint/gcodefiles.py b/octoprint/gcodefiles.py
index e34ae0a5..472a6ba1 100644
--- a/octoprint/gcodefiles.py
+++ b/octoprint/gcodefiles.py
@@ -129,23 +129,24 @@ class GcodeManager:
 		if not file or not destination:
 			return None, True
 
-		local = True if destination == FileDestinations.LOCAL else False
+		curaEnabled = self._settings.getBoolean(["cura", "enabled"])
+		filename = file.filename
 
-		absolutePath = self.getAbsolutePath(file.filename, mustExist=False)
+		absolutePath = self.getAbsolutePath(filename, mustExist=False)
+		gcode = isGcodeFileName(filename)
 
-		if absolutePath is None:
+		if absolutePath is None or (not curaEnabled and not gcode):
 			return None, True
 
 		file.save(absolutePath)
-		filename = file.filename
 
-		if isGcodeFileName(filename):
+		if gcode:
 			return self.processGcode(absolutePath), True
-
-		curaEnabled = self._settings.get(["cura", "enabled"])
-		if curaEnabled and isSTLFileName(filename) and local:
-			self.processStl(absolutePath)
-		return filename, False
+		else:
+			local = (destination == FileDestinations.LOCAL)
+			if curaEnabled and isSTLFileName(filename) and local:
+				self.processStl(absolutePath)
+			return filename, False
 
 
 	def getFutureFileName(self, file):
@@ -214,7 +215,7 @@ class GcodeManager:
 
 		if absolutePath is None:
 			return
-	
+
 		os.remove(absolutePath)
 		if os.path.exists(stlPath):
 			os.remove(stlPath)
@@ -455,7 +456,7 @@ class MetadataAnalyzer:
 
 	def _analyzeGcode(self, filename):
 		path = self._getPathCallback(filename)
-		if path is None:
+		if path is None or not os.path.exists(path):
 			return
 
 		self._currentFile = filename
diff --git a/octoprint/server.py b/octoprint/server.py
index 539696a6..82d34cf0 100644
--- a/octoprint/server.py
+++ b/octoprint/server.py
@@ -406,7 +406,7 @@ def uploadGcodeFile():
 			currentSd = currentJob["sd"]
 
 		futureFilename = gcodeManager.getFutureFilename(file)
-		if futureFilename is None:
+		if futureFilename is None or (not settings().getBoolean(["cura", "enabled"]) and not util.isGcodeFileName(futureFilename)):
 			return make_response("Can not upload file %s, wrong format?" % file.filename, 400)
 
 		if futureFilename == currentFilename and sd == currentSd and printer.isPrinting() or printer.isPaused():
diff --git a/octoprint/static/js/app/main.js b/octoprint/static/js/app/main.js
index 40aecf1e..afa168c7 100644
--- a/octoprint/static/js/app/main.js
+++ b/octoprint/static/js/app/main.js
@@ -65,7 +65,7 @@ $(function() {
         function gcode_upload_fail(e, data) {
             $.pnotify({
                 title: "Upload failed",
-                text: "<p>Could not upload the file. Make sure it is a GCODE file and has one of the following extensions: .gcode, .gco</p><p>Server reported: <pre>" + data.jqXHR.responseText + "</pre></p>",
+                text: "<p>Could not upload the file. Make sure that it is a GCODE file and has the extension \".gcode\" or \".gco\" or that it is an STL file with the extension \".stl\" and Cura support is enabled and configured.</p><p>Server reported: <pre>" + data.jqXHR.responseText + "</pre></p>",
                 type: "error",
                 hide: false
             });