diff --git a/README.markdown b/README.markdown
index cb7a50cda..ca0d9a6ff 100644
--- a/README.markdown
+++ b/README.markdown
@@ -87,8 +87,8 @@ The author of the Silk icon set is Mark James.
         --save <file>       Save configuration to the specified file
         --load <file>       Load configuration from the specified file. It can be used 
                             more than once to load options from multiple files.
-        -o, --output <file> File to output gcode to (by default, the file will be saved
-                            into the same directory as the input file using the 
+        -o, --output <file> File or directory to output gcode to (by default, the file will be
+                            saved into the same directory as the input file using the
                             --output-filename-format to generate the filename)
         -j, --threads <num> Number of threads to use (1+, default: 2)
     
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index 6cedfe7d6..3e81300d2 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -775,6 +775,10 @@ sub expanded_output_filepath {
     my $self = shift;
     my ($path) = @_;
     
+    # if output path is an existing directory, we take that and append
+    # the specified filename format
+    $path = File::Spec->join($path, $Slic3r::Config->output_filename_format) if ($path && -d $path);
+
     # if no explicit output file was defined, we take the input
     # file directory and append the specified filename format
     my $input_file = $self->objects->[0]->input_file;
diff --git a/utils/zsh/functions/_slic3r b/utils/zsh/functions/_slic3r
index 16d32e0eb..384c812a5 100644
--- a/utils/zsh/functions/_slic3r
+++ b/utils/zsh/functions/_slic3r
@@ -11,10 +11,10 @@ _arguments -S \
     '(- *)--version[output the version of Slic3r and exit]' \
     '--save[save configuration to file]:config output file:_files -g "*.(#i)ini(-.)"' \
     '*--load[load configuration from file]:config input file:_files -g "*.(#i)ini(-.)"' \
-    '(--output -o --output-filename-format)'{--output,-o}'[specify output file]:output file:_files -g "*.(#i)(gcode|svg)(-.)"' \
+    '(--output -o)'{--output,-o}'[specify output file]:output file:_files -g "*.(#i)(gcode|svg)(-.)"' \
     '(--threads -j)'{--threads,-j}'[specify number of threads to use]:number of threads' \
     \
-    '(--output -o)--output-filename-format[specify output filename format]:output filename format' \
+    '--output-filename-format[specify output filename format]:output filename format' \
     '*--post-process[specify post-processing script]:post-processing script file:_files' \
     '--export-svg[export SVG containing slices instead of G-code]' \
     '(--merge -m)'{--merge,-m}'[merge multiple input files into a single print]' \