diff --git a/ivette/Makefile.installation b/ivette/Makefile.installation
index 852e0a565883fe2a1ae1fabefda87109c473f429..7a69ff94f9cdf51f8e251481a32859576771b14f 100644
--- a/ivette/Makefile.installation
+++ b/ivette/Makefile.installation
@@ -24,32 +24,24 @@
 # --- OPAM Installation
 # --------------------------------------------------------------------------
 
-ifeq ($(INSTALLDIR),)
-IVETTE_PREFIX=$(OPAM_SWITCH_PREFIX)
-else
-IVETTE_PREFIX=$(INSTALLDIR)
-endif
-
-ifeq ($(IVETTE_PREFIX),)
-
+ifndef PREFIX
+then
 install::
 	@echo "Warning: not target for Ivette"
 	@echo "  (no INSTALLDIR, nor OPAM_SWITCH_PREFIX)"
-
 else
-
 install::
-	@echo "Installing Ivette to ${IVETTE_PREFIX}"
-	@mkdir -p ${IVETTE_PREFIX}/bin
-	@install ivette/ivette-bootstrap.sh ${IVETTE_PREFIX}/bin/ivette
-	@mkdir -p ${IVETTE_PREFIX}/lib/frama-c
-	@tar zcf ${IVETTE_PREFIX}/lib/frama-c/ivette.tgz ivette
+	@echo "Installing Ivette to ${PREFIX}"
+	@mkdir -p ${PREFIX}/bin
+	@install ivette/ivette-bootstrap.sh ${PREFIX}/bin/ivette
+	@mkdir -p ${PREFIX}/lib/frama-c
+	@tar zcf ${PREFIX}/lib/frama-c/ivette.tgz ivette
 
 uninstall::
 	@echo "Removing Ivette"
-	@rm -f ${IVETTE_PREFIX}/bin/ivette
-	@rm -f ${IVETTE_PREFIX}/lib/frama-c/ivette.tgz
-	@rm -fr ${IVETTE_PREFIX}/lib/frama-c/Ivette.app
-	@rm -fr ${IVETTE_PREFIX}/lib/frama-c/ivette
+	@rm -f ${PREFIX}/bin/ivette
+	@rm -f ${PREFIX}/lib/frama-c/ivette.tgz
+	@rm -fr ${PREFIX}/lib/frama-c/Ivette.app
+	@rm -fr ${PREFIX}/lib/frama-c/ivette
 
 endif
diff --git a/opam b/opam
index 274e43adb665ecbb2e18c7411e0084a09bdee349..6665291774815c5ff5c7735ac7f665f4ce13e3a2 100644
--- a/opam
+++ b/opam
@@ -97,7 +97,7 @@ install: [
 ]
 
 remove: [
-  [make "PREFIX=%{prefix}%" "-f" "ivette/makefile.opam" "uninstall"]
+  [make "PREFIX=%{prefix}%" "-f" "ivette/Makefile.installation" "uninstall"]
 ]
 
 run-test: [