diff --git a/src/fake_outputs.c b/src/fake_outputs.c
index 64c3e20c..39cbd7bb 100644
--- a/src/fake_outputs.c
+++ b/src/fake_outputs.c
@@ -28,8 +28,9 @@ static Output *get_screen_at(unsigned int x, unsigned int y) {
 /*
  * Creates outputs according to the given specification.
  * The specification must be in the format wxh+x+y, for example 1024x768+0+0,
+ * optionally followed by 'P' to indicate a primary output,
  * with multiple outputs separated by commas:
- *   1900x1200+0+0,1280x1024+1900+0
+ *   1900x1200+0+0P,1280x1024+1900+0
  *
  */
 void fake_outputs_init(const char *output_spec) {
@@ -37,8 +38,17 @@ void fake_outputs_init(const char *output_spec) {
     unsigned int x, y, width, height;
     int chars_consumed;
     while (sscanf(walk, "%ux%u+%u+%u%n", &width, &height, &x, &y, &chars_consumed) == 4) {
-        DLOG("Parsed output as width = %u, height = %u at (%u, %u)\n",
-             width, height, x, y);
+        walk += chars_consumed;
+        bool primary = false;
+        if (*walk == 'P') {
+            primary = true;
+            walk++;
+        }
+        if (*walk == ',')
+            walk++; /* Skip delimiter */
+        DLOG("Parsed output as width = %u, height = %u at (%u, %u)%s\n",
+             width, height, x, y, primary ? " (primary)" : "");
+
         Output *new_output = get_screen_at(x, y);
         if (new_output != NULL) {
             DLOG("Re-used old output %p\n", new_output);
@@ -67,10 +77,7 @@ void fake_outputs_init(const char *output_spec) {
             init_ws_for_output(new_output, output_get_content(new_output->con));
             num_screens++;
         }
-
-        walk += chars_consumed;
-        if (*walk == ',')
-            walk++;
+        new_output->primary = primary;
     }
 
     if (num_screens == 0) {