diff --git a/SConstruct b/SConstruct
index 975b10048..c84cd091f 100644
--- a/SConstruct
+++ b/SConstruct
@@ -1022,7 +1022,7 @@ def install(*args, **kwargs):
 
 env.SConsignFile()
 
-env.Append(CPPPATH=[],
+env.Prepend(CPPPATH=[],
            LIBPATH=[Dir('build/lib')])
 
 # preprocess input files (cti -> xml)
diff --git a/doc/sphinx/compiling.rst b/doc/sphinx/compiling.rst
index 348ddbe76..bb68b84a0 100644
--- a/doc/sphinx/compiling.rst
+++ b/doc/sphinx/compiling.rst
@@ -201,6 +201,9 @@ OS X
 
       CC=clang CXX=clang++
 
+* The Accelerate framework provides optimized versions of BLAS and LAPACK, so
+  the ``blas_lapack_libs`` option should generally be left unspecified.
+
 Intel Compilers
 ---------------
 * Before compiling Cantera, you may need to set up the appropriate environment
diff --git a/ext/SConscript b/ext/SConscript
index 7989ef318..f5bd4f088 100644
--- a/ext/SConscript
+++ b/ext/SConscript
@@ -8,13 +8,13 @@ def prep_default(env):
 
 def prep_fortran(env):
     localenv = env.Clone()
-    localenv.Append(CPPPATH='#include/cantera/base') # for config.h
+    localenv.Prepend(CPPPATH='#include/cantera/base') # for config.h
     return localenv
 
 def prep_f2c(env):
     localenv = env.Clone()
 
-    localenv.Append(CPPPATH=Dir('#ext/f2c_libs'))
+    localenv.Prepend(CPPPATH=Dir('#ext/f2c_libs'))
     if not localenv['HAS_TIMES_H']:
         localenv.Append(CPPDEFINES=['USE_CLOCK'])
     if not localenv['HAS_UNISTD_H']:
@@ -37,7 +37,7 @@ def prep_f2c(env):
 
 def prep_sundials(env):
     localenv = env.Clone()
-    localenv.Append(CPPPATH=Dir('#ext/cvode/include'))
+    localenv.Prepend(CPPPATH=Dir('#ext/cvode/include'))
 
     # Suppress warnings from external code
     if '-Wall' in localenv['CCFLAGS']:
@@ -47,8 +47,8 @@ def prep_sundials(env):
 
 def prep_gtest(env):
     localenv = env.Clone()
-    localenv.Append(CPPPATH=[Dir('#ext/gtest'),
-                             Dir('#ext/gtest/include')],
+    localenv.Prepend(CPPPATH=[Dir('#ext/gtest'),
+                              Dir('#ext/gtest/include')],
                     CPPDEFINES={'GTEST_HAS_PTHREAD': 0})
     return localenv
 
@@ -132,8 +132,8 @@ for subdir, extensions, prepFunction in libs:
 
 
 localenv = env.Clone()
-localenv.Append(CPPPATH=[Dir('#ext/gtest'),
-                         Dir('#ext/gtest/include')],
+localenv.Prepend(CPPPATH=[Dir('#ext/gtest'),
+                          Dir('#ext/gtest/include')],
                 CPPDEFINES={'GTEST_HAS_PTHREAD': 0})
 build(localenv.Library(pjoin('../lib', 'gtest'),
                        source=['gtest/src/gtest-all.cc']))
diff --git a/include/cantera/kinetics/RxnRates.h b/include/cantera/kinetics/RxnRates.h
index 2fe523d87..616100b57 100644
--- a/include/cantera/kinetics/RxnRates.h
+++ b/include/cantera/kinetics/RxnRates.h
@@ -422,7 +422,7 @@ public:
         Ea2_.resize(maxRates_);
 
         if (rdata.validate) {
-            validate();
+            validate(rdata);
         }
     }
 
@@ -514,7 +514,7 @@ public:
     //! temperatures at each interpolation pressure. This is potentially an
     //! issue when one of the Arrhenius expressions at a particular pressure
     //! has a negative pre-exponential factor.
-    void validate() {
+    void validate(const ReactionData& rdata) {
         double T[] = {1.0, 10.0, 100.0, 1000.0, 10000.0};
         for (pressureIter iter = pressures_.begin();
              iter->first < 1000;
@@ -528,9 +528,10 @@ public:
                     // message will correctly indicate that the problematic rate
                     // expression is at the higher of the adjacent pressures.
                     throw CanteraError("Plog::validate",
-                                       "Invalid rate coefficient at P = " +
-                                       fp2str(exp((++iter)->first)) +
-                                       ", T = " + fp2str(T[i]));
+                        "Invalid rate coefficient for reaction #" +
+                        int2str(rdata.number) + ":\n" + rdata.equation + "\n" +
+                        "at P = " + fp2str(exp((++iter)->first)) +
+                        ", T = " + fp2str(T[i]));
                 }
             }
         }
diff --git a/interfaces/python/ck2cti.py b/interfaces/python/ck2cti.py
index 02dd406ab..752acc5f8 100755
--- a/interfaces/python/ck2cti.py
+++ b/interfaces/python/ck2cti.py
@@ -60,6 +60,7 @@ UNIT_OPTIONS = {'CAL/': 'cal/mol',
                 'MOLEC': 'molec',
                 'MOLECULES': 'molec'}
 
+PROCESSED_UNITS = False
 ENERGY_UNITS = 'cal/mol'
 QUANTITY_UNITS = 'mol'
 
@@ -1342,8 +1343,16 @@ def loadChemkinFile(path, speciesList=None):
                 except IndexError:
                     pass
 
-                ENERGY_UNITS = UNIT_OPTIONS[energyUnits]
-                QUANTITY_UNITS = UNIT_OPTIONS[moleculeUnits]
+                global PROCESSED_UNITS, ENERGY_UNITS, UNIT_OPTIONS
+                if not PROCESSED_UNITS:
+                    PROCESSED_UNITS = True
+                    ENERGY_UNITS = UNIT_OPTIONS[energyUnits]
+                    QUANTITY_UNITS = UNIT_OPTIONS[moleculeUnits]
+                else:
+                    if (ENERGY_UNITS != UNIT_OPTIONS[energyUnits] or
+                        QUANTITY_UNITS != UNIT_OPTIONS[moleculeUnits]):
+                        raise InputParseError("Multiple REACTIONS sections with "
+                                              "different units are not supported.")
 
                 kineticsList = []
                 commentsList = []
diff --git a/src/SConscript b/src/SConscript
index 6eef5b17a..4e81fb772 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -38,8 +38,8 @@ libs = [('base', ['cpp'], baseSetup),
 
 for subdir, extensions, setup in libs:
     localenv = env.Clone()
-    localenv.Append(CPPPATH=Dir('#include'))
-    localenv.Append(CPPPATH=Dir('#src')) # todo: remove when not needed
+    localenv.Prepend(CPPPATH=Dir('#include'))
+    localenv.Prepend(CPPPATH=Dir('#src')) # todo: remove when not needed
     source = setup(localenv, subdir, extensions)
     objects = localenv.SharedObject(source)
     localenv.Depends(objects, localenv['config_h_target'])
diff --git a/src/apps/SConscript b/src/apps/SConscript
index 0a9752080..c0730c97f 100644
--- a/src/apps/SConscript
+++ b/src/apps/SConscript
@@ -2,7 +2,7 @@ from buildutils import *
 
 Import('env', 'build', 'install')
 localenv = env.Clone()
-localenv.Append(CPPPATH=['#src', '#include', '#src/apps'])
+localenv.Prepend(CPPPATH=['#src', '#include', '#src/apps'])
 
 def buildProgram(name, src):
     prog = build(localenv.Program(target=pjoin('#build/bin', name),
diff --git a/src/fortran/SConscript b/src/fortran/SConscript
index c2c3b91d0..f84cd4757 100644
--- a/src/fortran/SConscript
+++ b/src/fortran/SConscript
@@ -3,7 +3,7 @@ from buildutils import *
 Import('env', 'build', 'install')
 
 localenv = env.Clone()
-localenv.Append(CPPPATH=['#include', '#src'])
+localenv.Prepend(CPPPATH=['#include', '#src'])
 
 f90_src = mglob(localenv, '.', 'f90', 'cpp')
 
diff --git a/src/matlab/SConscript b/src/matlab/SConscript
index 8513e993d..5e7a628ba 100644
--- a/src/matlab/SConscript
+++ b/src/matlab/SConscript
@@ -53,8 +53,8 @@ elif os.name == 'posix':
     linkflags.extend(['-Wl,--no-undefined',
                       '-Wl,--version-script,src/matlab/mexFunction.map'])
 
-localenv.Append(CPPPATH=['#include', '#src', matlab_include],
-                CPPDEFINES=['MATLAB_MEX_FILE'],
+localenv.Prepend(CPPPATH=['#include', '#src', matlab_include])
+localenv.Append(CPPDEFINES=['MATLAB_MEX_FILE'],
                 LIBPATH=[matlab_libs],
                 LINKFLAGS=linkflags)
 
diff --git a/src/python/SConscript b/src/python/SConscript
index f96f6d47f..9bb4bad3c 100644
--- a/src/python/SConscript
+++ b/src/python/SConscript
@@ -31,7 +31,7 @@ make_setup = localenv.SubstFile('#interfaces/python/setup.py',
 
 extraArgs = ''
 if localenv['python_package'] == 'full':
-    localenv.Append(CPPPATH=['#src', '#include'])
+    localenv.Prepend(CPPPATH=['#src', '#include'])
 
     cantera_libname = 'cantera_shared' if os.name=='nt' else 'cantera'
     #pylinklibs = [cantera_libname, 'cvode', 'ctmath', 'ctlapack', 'ctblas', 'ctf2c', 'execstream']
diff --git a/test/SConscript b/test/SConscript
index aa32410ec..e4bd48ce6 100644
--- a/test/SConscript
+++ b/test/SConscript
@@ -4,9 +4,9 @@ import subprocess
 Import('env','build','install')
 localenv = env.Clone()
 
-localenv.Append(CPPPATH=['#ext/gtest/include', '#include'],
-                LIBPATH='#build/lib',
-                LIBS=['gtest'] + localenv['cantera_libs'])
+localenv.Prepend(CPPPATH=['#ext/gtest/include', '#include'],
+                 LIBPATH='#build/lib')
+localenv.Append(LIBS=['gtest'] + localenv['cantera_libs'])
 
 localenv['ENV']['PYTHONPATH'] = Dir('#interfaces/python').abspath
 localenv['ENV']['CANTERA_DATA'] = Dir('#build/data').abspath
diff --git a/test_problems/SConscript b/test_problems/SConscript
index 92f60dbdd..8317aa280 100644
--- a/test_problems/SConscript
+++ b/test_problems/SConscript
@@ -2,7 +2,7 @@ from buildutils import *
 
 Import('env','build','install')
 localenv = env.Clone()
-localenv.Append(CPPPATH=['#include', '#src', 'shared'])
+localenv.Prepend(CPPPATH=['#include', '#src', 'shared'])
 
 os.environ['PYTHONPATH'] = pjoin(os.getcwd(), '..', 'interfaces', 'python')
 os.environ['CANTERA_DATA'] = pjoin(os.getcwd(), '..', 'build', 'data')