diff --git a/history.txt b/history.txt
index 7a02a867..d00869d8 100755
--- a/history.txt
+++ b/history.txt
@@ -2017,3 +2017,4 @@ ______
 * Threads: Text comparisons are now case-sensitive („fixes“ #175)
 * Threads: fixed #179 - don’t identify primitive (static) C-Slots as implicit formal parameters
 * Threads: fixed #249 - preserve variable value types with edge cases (empty string, Boolean false)
+* Threads: fixed #133 - preserve edge-cased argument types (empty string, Boolean false)
diff --git a/threads.js b/threads.js
index 3ff7a50b..78831cf7 100644
--- a/threads.js
+++ b/threads.js
@@ -789,7 +789,7 @@ Process.prototype.evaluate = function (
         // assign formal parameters
         for (i = 0; i < context.inputs.length; i += 1) {
             value = 0;
-            if (parms[i]) {
+            if (!isNil(parms[i])) {
                 value = parms[i];
             }
             outer.variables.addVar(context.inputs[i], value);
@@ -858,7 +858,7 @@ Process.prototype.fork = function (context, args) {
         // assign formal parameters
         for (i = 0; i < context.inputs.length; i += 1) {
             value = 0;
-            if (parms[i]) {
+            if (!isNil(parms[i])) {
                 value = parms[i];
             }
             outer.variables.addVar(context.inputs[i], value);
@@ -1018,7 +1018,7 @@ Process.prototype.evaluateCustomBlock = function () {
         // assign formal parameters
         for (i = 0; i < context.inputs.length; i += 1) {
             value = 0;
-            if (parms[i]) {
+            if (!isNil(parms[i])) {
                 value = parms[i];
             }
             outer.variables.addVar(context.inputs[i], value);