diff --git a/Bootloaders/makefile b/Bootloaders/makefile
index 1a4d3457e01b8c65e97308fb5acfe0db9ef51117..003069b9ae7d4d67ef2aa3a6748e1c175115e244 100644
--- a/Bootloaders/makefile
+++ b/Bootloaders/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Demos/Device/ClassDriver/makefile b/Demos/Device/ClassDriver/makefile
index 797a483fa38bd768658da9b49682d6ce203d706c..776288f298e977d99aad1580d6e5a38fb56e8584 100644
--- a/Demos/Device/ClassDriver/makefile
+++ b/Demos/Device/ClassDriver/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Demos/Device/LowLevel/makefile b/Demos/Device/LowLevel/makefile
index 797a483fa38bd768658da9b49682d6ce203d706c..776288f298e977d99aad1580d6e5a38fb56e8584 100644
--- a/Demos/Device/LowLevel/makefile
+++ b/Demos/Device/LowLevel/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Demos/DualRole/ClassDriver/makefile b/Demos/DualRole/ClassDriver/makefile
index b9538fe3b805255f7d7015244d99d9f3defe43c6..6d16493ee994066bf358928434e4a816de30f6a0 100644
--- a/Demos/DualRole/ClassDriver/makefile
+++ b/Demos/DualRole/ClassDriver/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Demos/Host/ClassDriver/makefile b/Demos/Host/ClassDriver/makefile
index d057a1c698fc03ebb447e0de1aebc0b702db5f18..e33bf963bdd0fdb5f6e778fe66f3f14a8ea14967 100644
--- a/Demos/Host/ClassDriver/makefile
+++ b/Demos/Host/ClassDriver/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Demos/Host/LowLevel/makefile b/Demos/Host/LowLevel/makefile
index d057a1c698fc03ebb447e0de1aebc0b702db5f18..e33bf963bdd0fdb5f6e778fe66f3f14a8ea14967 100644
--- a/Demos/Host/LowLevel/makefile
+++ b/Demos/Host/LowLevel/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if
diff --git a/Projects/makefile b/Projects/makefile
index f4b411145ae59a0940e66582c4d2349cf04756a1..dd0ea2e8f5d6c2142d19c28f83cb11980f07ae0d 100644
--- a/Projects/makefile
+++ b/Projects/makefile
@@ -13,7 +13,7 @@
 # custom LUFA library build options are reflected in the compiled
 # code.
 
-PROJECT_DIRECTORIES = $(shell ls -d */)
+PROJECT_DIRECTORIES := $(shell ls -d */)
 
 # This makefile is potentially infinitely recursive if something really bad
 # happens when determining the set of project directories - hard-abort if