diff --git a/share/completions/mmdc.fish b/share/completions/mmdc.fish
index d94857514..68414fd23 100644
--- a/share/completions/mmdc.fish
+++ b/share/completions/mmdc.fish
@@ -19,7 +19,7 @@ complete -c $command -s h -l height -x \
 
 complete -c $command -s i -l input -r -d 'Specify the input file of a chart'
 complete -c $command -s o -l output -r \
-    -a '(__fish_print_extensions svg md png pdf)' \
+    -a '(__fish_complete_extensions svg\tdefault md png pdf)' \
     -d 'Specify the output file of a chart'
 
 complete -c $command -s e -l outputFormat -x \
diff --git a/share/functions/__fish_complete_extensions.fish b/share/functions/__fish_complete_extensions.fish
new file mode 100644
index 000000000..f39adb6ff
--- /dev/null
+++ b/share/functions/__fish_complete_extensions.fish
@@ -0,0 +1,16 @@
+function __fish_complete_extensions \
+    --description 'Suggest provided extensions as $argv if the current token ends with a dot'
+
+    set token (commandline -c -t)
+
+    switch "$token"
+        case '*.'
+            for extension in $argv
+                if string match --quiet --regex '\\\t|\t' -- $extension
+                    echo -e "$token$extension"
+                else
+                    printf "%s%s\n" $token $extension
+                end
+            end
+    end
+end
diff --git a/share/functions/__fish_print_extensions.fish b/share/functions/__fish_print_extensions.fish
deleted file mode 100644
index 2c1c20acc..000000000
--- a/share/functions/__fish_print_extensions.fish
+++ /dev/null
@@ -1,12 +0,0 @@
-function __fish_print_extensions \
-    --description 'Suggest provided extensions as $argv if the current token ends with a dot'
-
-    set token (commandline -c -t)
-
-    switch "$token"
-        case '*.'
-            for extension in $argv
-                printf "%s%s\n" $token $extension
-            end
-    end
-end