diff --git a/INIT/ftINITInternalAlg.m b/INIT/ftINITInternalAlg.m
index 19c0ddc4..0b990920 100644
--- a/INIT/ftINITInternalAlg.m
+++ b/INIT/ftINITInternalAlg.m
@@ -392,10 +392,17 @@
 metVarInd = (1:nMetabolMets) + (length(prob.vartype) - nMetVars);
 
 if allowExcretion
-    prob.csense = [repmat('L', 1, length(milpModel.mets)), ...
+    %S*v >= 0: a metabolite may be produced in excess of what is consumed,
+    %and the surplus is implicitly excreted. 'L' would say S*v <= 0, which
+    %lets a metabolite be consumed without ever being produced -- free
+    %uptake, the opposite of excretion, and enough for the MILP to switch a
+    %reaction on by conjuring its substrates out of nothing.
+    prob.csense = [repmat('G', 1, length(milpModel.mets)), ...
                   repmat('E', 1, length(prob.b) - length(milpModel.mets))];
 else
-    prob.csense = '=';
+    %One character per row: optimizeProb maps csense elementwise for glpk and
+    %cobra, so a scalar '=' only happens to work on gurobi.
+    prob.csense = repmat('E', 1, length(prob.b));
 end
 
 params.intTol = 10^-7; %This value is very important. If set too low
diff --git a/testing/function_tests/tINIT.m b/testing/function_tests/tINIT.m
index 5c77724c..71c5e1ac 100644
--- a/testing/function_tests/tINIT.m
+++ b/testing/function_tests/tINIT.m
@@ -259,6 +259,32 @@ function ftINITFullVsThreeStepRuns(testCase)
             testCase.verifyTrue(all(contains(mres2.rxns, expResult)));
         end
 
+        function ftINITSeriesVariantsRun(testCase)
+            % Only '1+1' and 'full' were ever exercised, so the 2-step series
+            % from the paper -- and the allowExcretion constraint they lean on
+            % -- had no coverage at all.
+            testCase.assumeMILPSolver();
+            testModel  = getTstModel();
+            testParams = struct();
+            evalc('prepData = prepINITModel(testModel, {}, {}, false, {}, ''s'');');
+            arrayData.genes     = testModel.genes;
+            arrayData.tissues   = {'a'};
+            arrayData.levels    = getExprForRxnScore(getTstModelRxnScores());
+            arrayData.threshold = 1;
+
+            steps = getINITSteps([], '2+1');
+            evalc(['resModel = ftINIT(prepData,arrayData.tissues{1},[],[],' ...
+                'arrayData,[],steps,true,true,testParams,false);']);
+            % Same answer as the '1+1' series in ftINITPipelineRuns.
+            testCase.verifyEqual(resModel.rxns, {'R1';'R4';'R6';'R8';'R9';'R10'});
+
+            steps = getINITSteps([], '2+0');
+            evalc(['resModel = ftINIT(prepData,arrayData.tissues{1},[],[],' ...
+                'arrayData,[],steps,true,true,testParams,false);']);
+            % '2+0' skips step 3, so the GPR-less transport R2 survives.
+            testCase.verifyEqual(resModel.rxns, {'R1';'R2';'R4';'R6';'R8';'R9';'R10'});
+        end
+
     end
 end