diff --git a/doc/builders/images/makediskimage.section.md b/doc/builders/images/makediskimage.section.md
index 833a6461e57b..c4566e753108 100644
--- a/doc/builders/images/makediskimage.section.md
+++ b/doc/builders/images/makediskimage.section.md
@@ -101,6 +101,7 @@ in
     diskSize = "auto";
     additionalSpace = "0M"; # Defaults to 512M.
     copyChannel = false;
+    memSize = 2048; # Qemu VM memory size in megabytes. Defaults to 1024M.
   }
 ```
 
diff --git a/nixos/lib/make-disk-image.nix b/nixos/lib/make-disk-image.nix
index 365fc1f03a5b..d641d1289fe4 100644
--- a/nixos/lib/make-disk-image.nix
+++ b/nixos/lib/make-disk-image.nix
@@ -154,6 +154,9 @@ To solve this, you can run `fdisk -l $image` and generate `dd if=$image of=$imag
 , # Shell code executed after the VM has finished.
   postVM ? ""
 
+, # Guest memory size
+  memSize ? 1024
+
 , # Copy the contents of the Nix store to the root of the image and
   # skip further setup. Incompatible with `contents`,
   # `installBootLoader` and `configFile`.
@@ -525,7 +528,7 @@ let format' = format; in let
           "-drive if=pflash,format=raw,unit=1,file=$efiVars"
         ]
       );
-      memSize = 1024;
+      inherit memSize;
     } ''
       export PATH=${binPath}:$PATH