diff --git a/.travis.yml b/.travis.yml
index 96f6f73b..ae6d8279 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -37,12 +37,6 @@ jobs:
         - PYDIST="ANACONDA"
         - FORTRAN="test"
       python: "3.9"
-    - name: "Ubuntu 18.04 + Python 3.6"
-      addons:
-        apt:
-          packages:
-            - gfortran
-      python: "3.6"
     - name: "Ubuntu 20.04 + Python 3.8"
       dist: focal
       addons:
diff --git a/camb/cambdll.dll b/camb/cambdll.dll
index 44e03d56..42cbe24d 100644
Binary files a/camb/cambdll.dll and b/camb/cambdll.dll differ
diff --git a/camb/dark_energy.py b/camb/dark_energy.py
index 6da78622..d3ef5036 100644
--- a/camb/dark_energy.py
+++ b/camb/dark_energy.py
@@ -51,6 +51,10 @@ def set_params(self, w=-1.0, wa=0, cs2=1.0):
         self.cs2 = cs2
         self.validate_params()
 
+    def validate_params(self):
+        if not self.use_tabulated_w and self.wa + self.w > 0:
+            raise CAMBError('dark energy model has w + wa > 0, giving w>0 at high redshift')
+
     def set_w_a_table(self, a, w):
         """
         Set w(a) from numerical values (used as cublic spline). Note this is quite slow.
@@ -80,8 +84,10 @@ class DarkEnergyFluid(DarkEnergyEqnOfState):
     _fortran_class_name_ = 'TDarkEnergyFluid'
 
     def validate_params(self):
-        if not self.use_tabulated_w and self.wa and (self.w < -1 - 1e-6 or 1 + self.w + self.wa < - 1e-6):
-            raise CAMBError('fluid dark energy model does not support w crossing -1')
+        super().validate_params()
+        if not self.use_tabulated_w:
+            if self.wa and (self.w < -1 - 1e-6 or 1 + self.w + self.wa < - 1e-6):
+                raise CAMBError('fluid dark energy model does not support w crossing -1')
 
 
 @fortran_class
diff --git a/fortran/DarkEnergyInterface.f90 b/fortran/DarkEnergyInterface.f90
index d7b6742e..671176aa 100644
--- a/fortran/DarkEnergyInterface.f90
+++ b/fortran/DarkEnergyInterface.f90
@@ -260,6 +260,10 @@ subroutine TDarkEnergyEqnOfState_ReadParams(this, Ini)
     if(.not. this%use_tabulated_w)then
         this%w_lam = Ini%Read_Double('w', -1.d0)
         this%wa = Ini%Read_Double('wa', 0.d0)
+        ! trap dark energy becoming important at high redshift 
+        ! (will still work if this test is removed in some cases)
+        if (this%w_lam + this%wa > 0) &
+             error stop 'w + wa > 0, giving w>0 at high redshift'
     else
         call File%LoadTxt(Ini%Read_String('wafile'), table)
         call this%SetwTable(table(:,1),table(:,2), size(table(:,1)))
diff --git a/fortran/cmbmain.f90 b/fortran/cmbmain.f90
index 8939ac0a..9ddba817 100644
--- a/fortran/cmbmain.f90
+++ b/fortran/cmbmain.f90
@@ -100,7 +100,7 @@ module CAMBmain
     integer maximum_l !Max value of l to compute
     real(dl) :: maximum_qeta = 3000._dl
 
-    integer :: l_smooth_sample = 3000 !assume transfer functions effectively small for k>2*l_smooth_sample
+    integer :: l_smooth_sample = 3000 !assume transfer functions effectively small for k*chi0>2*l_smooth_sample
 
     integer :: max_bessels_l_index  = 1000000
     real(dl) :: max_bessels_etak = 1000000*2
@@ -874,6 +874,7 @@ subroutine SetkValuesForSources
 
     q_cmb = 2*l_smooth_sample/State%chi0*SourceAccuracyBoost  !assume everything is smooth at l > l_smooth_sample
     if (CP%Want_CMB .and. maximum_l > 5000 .and. CP%Accuracy%AccuratePolarization) q_cmb = q_cmb*1.4
+    q_cmb = max(q_switch*2, q_cmb)
     !prevent EE going wild in tail
     dksmooth = q_cmb/2/(SourceAccuracyBoost)**2
     if (CP%Want_CMB) dksmooth = dksmooth/6
@@ -881,7 +882,8 @@ subroutine SetkValuesForSources
     associate(Evolve_q => ThisSources%Evolve_q)
         call Evolve_q%Init()
         call Evolve_q%Add_delta(qmin, qmax_log, dlnk0, IsLog = .true.)
-        call Evolve_q%Add_delta(qmax_log, min(qmax,q_switch), dkn1)
+        if (qmax > qmax_log) &
+            call Evolve_q%Add_delta(qmax_log, min(qmax,q_switch), dkn1)
         if (qmax > q_switch) then
             call Evolve_q%Add_delta(q_switch, min(q_cmb,qmax), dkn2)
             if (qmax > q_cmb) then
diff --git a/setup.py b/setup.py
index 5d4b8895..174c7fec 100644
--- a/setup.py
+++ b/setup.py
@@ -299,12 +299,11 @@ def run(self):
               'Intended Audience :: Science/Research',
               'Topic :: Scientific/Engineering :: Astronomy',
               'Programming Language :: Python :: 3',
-              'Programming Language :: Python :: 3.6',
               'Programming Language :: Python :: 3.7',
               'Programming Language :: Python :: 3.8',
               'Programming Language :: Python :: 3.9'
           ],
           keywords=['cosmology', 'CAMB', 'CMB'],
           install_requires=['scipy>=1.0', 'sympy>=1.0'],
-          python_requires='>=3.6'
+          python_requires='>=3.7'
           )