diff --git a/share/Makefile.common b/share/Makefile.common
index 8754621da7b77f997fcd326615908992472087f9..9df6e730ee14759532d4f61f964b483d9e5ac258 100644
--- a/share/Makefile.common
+++ b/share/Makefile.common
@@ -54,12 +54,16 @@ PLATFORM:=$(shell uname -s)
 #############
 
 ifndef PREFIX
+ifdef FRAMAC_INSTALLDIR
+PREFIX=$(FRAMAC_INSTALLDIR)
+else
 ifdef OPAM_SWITCH_PREFIX
 PREFIX=$(OPAM_SWITCH_PREFIX)
 else
 PREFIX=/usr/local
 endif
 endif
+endif
 
 #############
 # Verbosing #