diff --git a/jquery.flot.categories.js b/jquery.flot.categories.js
index 1716584..3003752 100644
--- a/jquery.flot.categories.js
+++ b/jquery.flot.categories.js
@@ -110,11 +110,14 @@ as "categories" on the axis object, e.g. plot.getAxes().xaxis.categories.
     }
 
     function categoriesTickGenerator(axis) {
-        var res = [];
-        for (var label in axis.categories) {
-            var v = axis.categories[label];
-            if (v >= axis.min && v <= axis.max) {
-                res.push([v, label]);
+        var res = [],
+            categories = axis.categories;
+        for (var label in categories) {
+            if (Object.prototype.hasOwnProperty.call(categories, label)) {
+                var v = categories[label];
+                if (v >= axis.min && v <= axis.max) {
+                    res.push([v, label]);
+                }
             }
         }
 
@@ -138,7 +141,9 @@ as "categories" on the axis object, e.g. plot.getAxes().xaxis.categories.
             }
             else {
                 for (var v in o) {
-                    c[v] = o[v];
+                    if (Object.prototype.hasOwnProperty.call(o, v)) {
+                        c[v] = o[v];
+                    }
                 }
             }
 
diff --git a/jquery.flot.js b/jquery.flot.js
index 1a4e261..4f577b0 100644
--- a/jquery.flot.js
+++ b/jquery.flot.js
@@ -1552,13 +1552,15 @@ Licensed under the MIT license.
         function setupGrid() {
             var axes = allAxes(),
                 showGrid = options.grid.show,
+                margin = options.grid.margin || 0,
                 i, a;
 
             // Initialize the plot's offset from the edge of the canvas
 
             for (a in plotOffset) {
-                var margin = options.grid.margin || 0;
-                plotOffset[a] = typeof margin === "number" ? margin : margin[a] || 0;
+                if (Object.prototype.hasOwnProperty.call(plotOffset, a)) {
+                    plotOffset[a] = typeof margin === "number" ? margin : margin[a] || 0;
+                }
             }
 
             executeHooks(hooks.processOffset, [plotOffset]);
diff --git a/jquery.flot.selection.js b/jquery.flot.selection.js
index 1d89ace..1fc33dc 100644
--- a/jquery.flot.selection.js
+++ b/jquery.flot.selection.js
@@ -237,16 +237,18 @@ The plugin allso adds the following methods to the plot object:
             var axis, from, to, key, axes = plot.getAxes();
 
             for (var k in axes) {
-                axis = axes[k];
-                if (axis.direction === coord) {
-                    key = coord + axis.n + "axis";
-                    if (!ranges[key] && axis.n === 1) {
-                        key = coord + "axis"; // support x1axis as xaxis
-                    }
-                    if (ranges[key]) {
-                        from = ranges[key].from;
-                        to = ranges[key].to;
-                        break;
+                if (Object.prototype.hasOwnProperty.call(axes, k)) {
+                    axis = axes[k];
+                    if (axis.direction === coord) {
+                        key = coord + axis.n + "axis";
+                        if (!ranges[key] && axis.n === 1) {
+                            key = coord + "axis"; // support x1axis as xaxis
+                        }
+                        if (ranges[key]) {
+                            from = ranges[key].from;
+                            to = ranges[key].to;
+                            break;
+                        }
                     }
                 }
             }