diff --git a/src/compile.js b/src/compile.js
index 6f1206b152..be0233f1ed 100644
--- a/src/compile.js
+++ b/src/compile.js
@@ -236,9 +236,12 @@ Compiler.prototype.outputInterruptTest = function () { // Added by RNL
     return output;
 };
 
-Compiler.prototype._jumpfalse = function (test, block) {
-    var cond = this._gr("jfalse", "(", test, "===false||!Sk.misceval.isTrue(", test, "))");
-    out("if(", cond, "){/*test failed */$blk=", block, ";continue;}");
+Compiler.prototype._jumpfalse = function (test, block, canSuspend) {
+    out("$ret=Sk.misceval.isTrue(", test, (canSuspend ? ",true" : "")+ ");");
+    if (canSuspend) {
+        this._checkSuspension(null, "$ret !== true && $ret !== false");
+    }    
+    out("if(!$ret){/*test failed */$blk=", block, ";continue;}");
 };
 
 Compiler.prototype._jumpundef = function (test, block) {
@@ -264,8 +267,9 @@ Compiler.prototype._jump = function (block) {
 /**
  * @param {Object=} e Object with keys 'lineno' and 'col_offset'
  */
-Compiler.prototype._checkSuspension = function(e) {
+Compiler.prototype._checkSuspension = function(e, suspCheck) {
     var retblk;
+    suspCheck = suspCheck ? suspCheck + " && " : "";
     if (this.u.canSuspend) {
 
         retblk = this.newBlock("function return or resume suspension");
@@ -274,13 +278,13 @@ Compiler.prototype._checkSuspension = function(e) {
 
         e = e || {lineno: "$currLineNo", col_offset: "$currColNo"};
 
-        out ("if ($ret && $ret.$isSuspension) { return $saveSuspension($ret,'"+this.filename+"',"+e.lineno+","+e.col_offset+"); }");
+        out ("if (" + suspCheck + "$ret !== undefined && $ret !== null && $ret.$isSuspension) { return $saveSuspension($ret,'"+this.filename+"',"+e.lineno+","+e.col_offset+"); }");
 
         this.u.doesSuspend = true;
         this.u.tempsToSave = this.u.tempsToSave.concat(this.u.localtemps);
 
     } else {
-        out ("if ($ret && $ret.$isSuspension) { $ret = Sk.misceval.retryOptionalSuspensionOrThrow($ret); }");
+        out ("if (" + suspCheck + "$ret !== undefined && $ret !== null && $ret.$isSuspension) { $ret = Sk.misceval.retryOptionalSuspensionOrThrow($ret); }");
     }
 };
 Compiler.prototype.cunpackstarstoarray = function(elts, permitEndOnly) {
@@ -510,7 +514,7 @@ Compiler.prototype.ccompgen = function (type, tmpname, generators, genIndex, val
     n = l.ifs ? l.ifs.length : 0;
     for (i = 0; i < n; ++i) {
         ifres = this.vexpr(l.ifs[i]);
-        this._jumpfalse(ifres, start);
+        this._jumpfalse(ifres, start, true);
     }
 
     if (++genIndex < generators.length) {
@@ -570,10 +574,12 @@ Compiler.prototype.ccompare = function (e) {
 
     for (i = 0; i < n; ++i) {
         rhs = this.vexpr(e.comparators[i]);
-        out("$ret = Sk.builtin.bool(Sk.misceval.richCompareBool(", cur, ",", rhs, ",'", e.ops[i].prototype._astname, "', true));");
+        out("$ret = Sk.misceval.richCompareBool(", cur, ",", rhs, ",'", e.ops[i].prototype._astname, "', true);");
         this._checkSuspension(e);
-        out(fres, "=$ret;");
-        this._jumpfalse("$ret", done);
+        out(fres, "=Sk.builtin.bool($ret);");
+        if (i < n - 1) {
+            this._jumpfalse("$ret", done, false);
+        }        
         cur = rhs;
     }
     this._jump(done);
@@ -1268,14 +1274,14 @@ Compiler.prototype.cif = function (s) {
         test = this.vexpr(s.test);
 
         if (s.orelse && s.orelse.length > 0) {
-            this._jumpfalse(test, next);
+            this._jumpfalse(test, next, true);
             this.vseqstmt(s.body);
             this._jump(end);
 
             this.setBlock(next);
             this.vseqstmt(s.orelse);
         } else {
-            this._jumpfalse(test, end);
+            this._jumpfalse(test, end, true);
             this.vseqstmt(s.body);
         }
         this._jump(end);
@@ -1304,7 +1310,7 @@ Compiler.prototype.cwhile = function (s) {
         body = this.newBlock("while body");
 
         this.annotateSource(s);
-        this._jumpfalse(this.vexpr(s.test), orelse ? orelse : next);
+        this._jumpfalse(this.vexpr(s.test), orelse ? orelse : next, true);
         this._jump(body);
 
         this.pushBreakBlock(next);
@@ -2199,7 +2205,7 @@ Compiler.prototype.cifexp = function (e) {
     var ret = this._gr("res", "null");
 
     var test = this.vexpr(e.test);
-    this._jumpfalse(test, next);
+    this._jumpfalse(test, next, true);
 
     out(ret, "=", this.vexpr(e.body), ";");
     this._jump(end);
diff --git a/src/misceval.js b/src/misceval.js
index cb6bc65b32..d817751e15 100644
--- a/src/misceval.js
+++ b/src/misceval.js
@@ -615,7 +615,7 @@ Sk.exportSymbol("Sk.misceval.opAllowsEquality", Sk.misceval.opAllowsEquality);
  * @returns {boolean}
  * @param {*} x 
  */
-Sk.misceval.isTrue = function (x) {
+Sk.misceval.isTrue = function (x, canSuspend) {
     if (x === true || x === Sk.builtin.bool.true$) {
         return true;
     }
@@ -626,11 +626,11 @@ Sk.misceval.isTrue = function (x) {
         return false;
     }
     if (x.nb$bool) {
-        return x.nb$bool(); // the slot wrapper takes care of converting to js Boolean
+        return x.nb$bool(canSuspend); // the slot wrapper takes care of converting to js Boolean
     }
     if (x.sq$length) {
         // the slot wrapper takes care of the error message and converting to js int
-        return x.sq$length() !== 0;
+        return Sk.misceval.chain(x.sq$length(canSuspend), (r) => r !== 0);
     }
     return Boolean(x);
 };
diff --git a/src/slotdefs.js b/src/slotdefs.js
index 4a163fe8e9..9961f9f412 100644
--- a/src/slotdefs.js
+++ b/src/slotdefs.js
@@ -135,25 +135,28 @@ function slotFuncNoArgs(dunderFunc) {
  */
 function slotFuncNoArgsWithCheck(dunderName, checkFunc, checkMsg, f) {
     return function (dunderFunc) {
-        return function () {
+        return function slotfunc(canSuspend) {
             const func = dunderFunc.tp$descr_get ? dunderFunc.tp$descr_get(this) : dunderFunc;
-            let res = Sk.misceval.callsimArray(func, []);
-            if (!checkFunc(res)) {
-                throw new Sk.builtin.TypeError(dunderName + " should return " + checkMsg + " (returned " + Sk.abstr.typeName(res) + ")");
-            }
-            // f is might be a function that changes the result to a js object like for nb$bool which returns a Boolean
-            if (f !== undefined) {
-                return f(res);
-            }
-            return res;
+            const ret = Sk.misceval.chain(Sk.misceval.callsimOrSuspendArray(func, []), (res) => {
+                if (checkFunc && !checkFunc(res)) {
+                    throw new Sk.builtin.TypeError(dunderName + " should return " + checkMsg + " (returned " + Sk.abstr.typeName(res) + ")");
+                }
+                // f might be a function that changes the result to a js object like for nb$bool which returns a Boolean
+                if (f !== undefined) {
+                    return f(res);
+                }
+                return res;
+            });
+            return canSuspend ? ret : Sk.misceval.retryOptionalSuspensionOrThrow(ret);
         };
     };
 }
 
 function slotFuncOneArg(dunderFunc) {
-    return function (value) {
+    return function (value, canSuspend) {
         const func = dunderFunc.tp$descr_get ? dunderFunc.tp$descr_get(this) : dunderFunc;
-        return Sk.misceval.callsimArray(func, [value]);
+        const ret = Sk.misceval.callsimOrSuspendArray(func, [value]);
+        return canSuspend ? ret : Sk.misceval.retryOptionalSuspensionOrThrow(ret);
     };
 }
 
@@ -846,21 +849,7 @@ slots.__next__ = {
 slots.__len__ = {
     $name: "__len__",
     $slot_name: "sq$length",
-    $slot_func: function (dunderFunc) {
-        return function sq$length(canSuspend) {
-            let res;
-            const func = dunderFunc.tp$descr_get ? dunderFunc.tp$descr_get(this) :  dunderFunc;
-            if (canSuspend) {
-                res = Sk.misceval.callsimOrSuspendArray(func, []);
-                return Sk.misceval.chain(res, (r) => {
-                    return Sk.misceval.asIndexOrThrow(r);
-                });
-            } else {
-                res = Sk.misceval.callsimArray(func, []);
-                return Sk.misceval.asIndexOrThrow(res);
-            }
-        };
-    },
+    $slot_func: slotFuncNoArgsWithCheck(null, null, null, (r) => Sk.misceval.asIndexOrThrow(r)), // asIndexOrThrow does the checks and conversion
     $wrapper: wrapperCallBack(wrapperCallNoArgs, (res) => new Sk.builtin.int_(res)),
     $flags: { NoArgs: true },
     $textsig: "($self, /)",
@@ -886,7 +875,7 @@ slots.__contains__ = {
             const func = dunderFunc.tp$descr_get ? dunderFunc.tp$descr_get(this) :  dunderFunc;
             let res = Sk.misceval.callsimOrSuspendArray(func, [key]);
             res = Sk.misceval.chain(res, (r) => Sk.misceval.isTrue(r));
-            if (res.$isSuspension) {
+            if (res !== true && res !== false && res.$isSuspension) {
                 return canSuspend ? res : Sk.misceval.retryOptionalSuspensionOrThrow(res);
             }
             return res;
@@ -912,13 +901,7 @@ slots.__contains__ = {
 slots.__getitem__ = {
     $name: "__getitem__",
     $slot_name: "mp$subscript",
-    $slot_func: function (dunderFunc) {
-        return function mp$subscript(key, canSuspend) {
-            const func = dunderFunc.tp$descr_get ? dunderFunc.tp$descr_get(this) :  dunderFunc;
-            const ret = Sk.misceval.callsimOrSuspendArray(func, [key]);
-            return canSuspend ? ret : Sk.misceval.retryOptionalSuspensionOrThrow(ret);
-        };
-    },
+    $slot_func: slotFuncOneArg,
     $wrapper: wrapperCallOneArg,
     $textsig: "($self, key, /)",
     $flags: { OneArg: true },