diff --git a/tests/builders.scm b/tests/builders.scm
index 8d2d75aa7f..d79603f7da 100644
--- a/tests/builders.scm
+++ b/tests/builders.scm
@@ -34,6 +34,10 @@ (define-module (test-builders)
 (define %store
   (false-if-exception (open-connection)))
 
+(when %store
+  ;; Make sure we build everything by ourselves.
+  (set-build-options %store #:use-substitutes? #f))
+
 (define %bootstrap-inputs
   ;; Use the bootstrap inputs so it doesn't take ages to run these tests.
   ;; This still involves building Make, Diffutils, and Findutils.
diff --git a/tests/derivations.scm b/tests/derivations.scm
index 2497fa8ec6..02f0a9b2a1 100644
--- a/tests/derivations.scm
+++ b/tests/derivations.scm
@@ -39,6 +39,9 @@ (define %store
   (false-if-exception (open-connection)))
 
 (when %store
+  ;; Make sure we build everything by ourselves.
+  (set-build-options %store #:use-substitutes? #f)
+
   ;; By default, use %BOOTSTRAP-GUILE for the current system.
   (let ((drv (package-derivation %store %bootstrap-guile)))
     (%guile-for-build drv)))
diff --git a/tests/packages.scm b/tests/packages.scm
index 005e605e83..8c2e6b9d08 100644
--- a/tests/packages.scm
+++ b/tests/packages.scm
@@ -35,6 +35,10 @@ (define-module (test-packages)
 (define %store
   (false-if-exception (open-connection)))
 
+(when %store
+  ;; Make sure we build everything by ourselves.
+  (set-build-options %store #:use-substitutes? #f))
+
 (define %bootstrap-inputs
   ;; Use the bootstrap inputs so it doesn't take ages to run these tests.
   ;; This still involves building GNU Make and GNU Diffutils.