diff --git a/README.md b/README.md
index 1298ba2..713ce94 100644
--- a/README.md
+++ b/README.md
@@ -35,8 +35,9 @@ Supported input formats are PNG, PDF, GIF, TIF, JPEG.
 
 Supported output formats are PNG, GIF, JPEG, TIFF.
 
-Output formats are determined by the provided filename extension,
-falling back to PNG.
+Output formats are determined by the provided filename extension.
+If no extension is provided, pngpaste infers the format from the
+clipboard input and appends an extension automatically.
 
 It's unclear if EXIF data in JPEG sources are preserved. There's an
 issue with pasting into JPEG format from a GIF source.
diff --git a/pngpaste.m b/pngpaste.m
index 4651c89..c1302da 100644
--- a/pngpaste.m
+++ b/pngpaste.m
@@ -8,7 +8,7 @@
 usage ()
 {
     fprintf(stderr,
-        "Usage: %s [OPTIONS] <dest.png>\n"
+        "Usage: %s [OPTIONS] <dest.png | dest>\n"
         "\t-\t" "Print to standard output" "\n"
         "\t-b\t" "Print to standard output as base64" "\n"
         "\t-v\t" "Version" "\n"
@@ -129,6 +129,54 @@
     return bitmapImageFileType;
 }
 
+BOOL
+hasFilenameExtension (NSString *filename)
+{
+    if (filename == nil) {
+        return NO;
+    }
+    return [[filename pathExtension] length] > 0;
+}
+
+NSBitmapImageFileType
+getBitmapImageFileTypeFromPasteboard (NSPasteboard *pasteBoard)
+{
+    NSBitmapImageFileType bitmapImageFileType = NSBitmapImageFileTypePNG;
+    if (pasteBoard != nil) {
+        NSArray *types = [pasteBoard types];
+        for (NSString *type in types) {
+            if ([type isEqualToString:@"public.jpeg"]) {
+                return NSBitmapImageFileTypeJPEG;
+            } else if ([type isEqualToString:NSPasteboardTypePNG]) {
+                return NSBitmapImageFileTypePNG;
+            } else if ([type isEqualToString:@"com.compuserve.gif"]) {
+                return NSBitmapImageFileTypeGIF;
+            } else if ([type isEqualToString:NSPasteboardTypeTIFF]) {
+                return NSBitmapImageFileTypeTIFF;
+            } else if ([type isEqualToString:NSPasteboardTypePDF]) {
+                return NSBitmapImageFileTypePNG;
+            }
+        }
+    }
+    return bitmapImageFileType;
+}
+
+NSString *
+extensionForBitmapImageFileType (NSBitmapImageFileType bitmapImageFileType)
+{
+    switch (bitmapImageFileType) {
+    case NSBitmapImageFileTypeGIF:
+        return @"gif";
+    case NSBitmapImageFileTypeJPEG:
+        return @"jpg";
+    case NSBitmapImageFileTypeTIFF:
+        return @"tiff";
+    case NSBitmapImageFileTypePNG:
+    default:
+        return @"png";
+    }
+}
+
 /*
  * Returns NSData from Pasteboard Image if available; otherwise nil
  */
@@ -209,8 +257,18 @@
         return EXIT_SUCCESS;
     }
 
-    NSBitmapImageFileType bitmapImageFileType =
-        getBitmapImageFileTypeFromFilename(params.outputFile);
+    NSPasteboard *pasteBoard = [NSPasteboard generalPasteboard];
+    NSString *outputFile = params.outputFile;
+    NSBitmapImageFileType bitmapImageFileType;
+    if (hasFilenameExtension(outputFile)) {
+        bitmapImageFileType = getBitmapImageFileTypeFromFilename(outputFile);
+    } else {
+        bitmapImageFileType = getBitmapImageFileTypeFromPasteboard(pasteBoard);
+        if (outputFile != nil) {
+            NSString *extension = extensionForBitmapImageFileType(bitmapImageFileType);
+            outputFile = [outputFile stringByAppendingPathExtension:extension];
+        }
+    }
     NSData *imageData = getPasteboardImageData(bitmapImageFileType);
     int exitCode;
 
@@ -227,7 +285,7 @@
             [stdout writeData:base64Data];
             exitCode = EXIT_SUCCESS;
         } else {
-            if ([imageData writeToFile:params.outputFile atomically:YES]) {
+            if ([imageData writeToFile:outputFile atomically:YES]) {
                 exitCode = EXIT_SUCCESS;
             } else {
                 fatal("Could not write to file!");