diff --git a/var/spack/repos/builtin/packages/flex/package.py b/var/spack/repos/builtin/packages/flex/package.py
index 0d720d307c..6718569586 100644
--- a/var/spack/repos/builtin/packages/flex/package.py
+++ b/var/spack/repos/builtin/packages/flex/package.py
@@ -34,9 +34,8 @@ class Flex(AutotoolsPackage):
 
     version('2.6.4', '2882e3179748cc9f9c23ec593d6adc8d')
     version('2.6.3', 'a5f65570cd9107ec8a8ec88f17b31bb1')
-    # Problematic version:
+    # Avoid flex '2.6.2' (major bug)
     # See issue #2554; https://github.com/westes/flex/issues/113
-    # version('2.6.2', 'cc6d76c333db7653d5caf423a3335239')
     version('2.6.1', '05bcd8fb629e0ae130311e8a6106fa82')
     version('2.6.0', '760be2ee9433e822b6eb65318311c19d')
     version('2.5.39', '5865e76ac69c05699f476515592750d7')
diff --git a/var/spack/repos/builtin/packages/foam-extend/package.py b/var/spack/repos/builtin/packages/foam-extend/package.py
index 91837af720..a6776b182f 100644
--- a/var/spack/repos/builtin/packages/foam-extend/package.py
+++ b/var/spack/repos/builtin/packages/foam-extend/package.py
@@ -100,7 +100,7 @@ class FoamExtend(Package):
     depends_on('mpi')
     depends_on('python')
     depends_on('zlib')
-    depends_on('flex@:2.6.1')  # <- restriction due to scotch
+    depends_on('flex',  type='build')
     depends_on('cmake', type='build')
 
     depends_on('scotch~metis',     when='~ptscotch+scotch')
diff --git a/var/spack/repos/builtin/packages/openfoam-com/package.py b/var/spack/repos/builtin/packages/openfoam-com/package.py
index ce7be181b5..9e930535a0 100644
--- a/var/spack/repos/builtin/packages/openfoam-com/package.py
+++ b/var/spack/repos/builtin/packages/openfoam-com/package.py
@@ -291,7 +291,7 @@ class OpenfoamCom(Package):
     depends_on('fftw')
     depends_on('boost')
     depends_on('cgal')
-    depends_on('flex@:2.6.1')  # <- restriction due to scotch
+    depends_on('flex',  type='build')
     depends_on('cmake', type='build')
 
     # Require scotch with ptscotch - corresponds to standard OpenFOAM setup
diff --git a/var/spack/repos/builtin/packages/openfoam-org/package.py b/var/spack/repos/builtin/packages/openfoam-org/package.py
index 017f6cc232..a31cc2e210 100644
--- a/var/spack/repos/builtin/packages/openfoam-org/package.py
+++ b/var/spack/repos/builtin/packages/openfoam-org/package.py
@@ -91,7 +91,7 @@ class OpenfoamOrg(Package):
     provides('openfoam')
     depends_on('mpi')
     depends_on('zlib')
-    depends_on('flex@:2.6.1')  # <- restriction due to scotch
+    depends_on('flex',  type='build')
     depends_on('cmake', type='build')
 
     # Require scotch with ptscotch - corresponds to standard OpenFOAM setup
diff --git a/var/spack/repos/builtin/packages/scotch/package.py b/var/spack/repos/builtin/packages/scotch/package.py
index b1aaad0eb6..c776e8560d 100644
--- a/var/spack/repos/builtin/packages/scotch/package.py
+++ b/var/spack/repos/builtin/packages/scotch/package.py
@@ -51,7 +51,8 @@ class Scotch(Package):
     variant('int64', default=False,
             description='Use int64_t for SCOTCH_Num typedef')
 
-    depends_on('flex@:2.6.1', type='build')
+    # Does not build with flex 2.6.[23]
+    depends_on('flex@:2.6.1,2.6.4:', type='build')
     depends_on('bison', type='build')
     depends_on('mpi', when='+mpi')
     depends_on('zlib', when='+compression')