diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f182ce899ce..8b53ecbf191 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7669,17 +7669,18 @@ namespace ts {
                     const type = flow.kind === FlowKind.LoopLabel ?
                         getTypeAtFlowNodeCached(antecedent) :
                         getTypeAtFlowNode(antecedent);
-                    if (type) {
-                        // If the type at a particular antecedent path is the declared type and the
-                        // reference is known to always be assigned (i.e. when declared and initial types
-                        // are the same), there is no reason to process more antecedents since the only
-                        // possible outcome is subtypes that will be removed in the final union type anyway.
-                        if (type === declaredType && declaredType === initialType) {
-                            return type;
-                        }
-                        if (!contains(antecedentTypes, type)) {
-                            antecedentTypes.push(type);
-                        }
+                    if (!type) {
+                        break;
+                    }
+                    // If the type at a particular antecedent path is the declared type and the
+                    // reference is known to always be assigned (i.e. when declared and initial types
+                    // are the same), there is no reason to process more antecedents since the only
+                    // possible outcome is subtypes that will be removed in the final union type anyway.
+                    if (type === declaredType && declaredType === initialType) {
+                        return type;
+                    }
+                    if (!contains(antecedentTypes, type)) {
+                        antecedentTypes.push(type);
                     }
                 }
                 return antecedentTypes.length === 0 ? undefined :
diff --git a/tests/baselines/reference/controlFlowLoopAnalysis.errors.txt b/tests/baselines/reference/controlFlowLoopAnalysis.errors.txt
new file mode 100644
index 00000000000..21bf6b1c19a
--- /dev/null
+++ b/tests/baselines/reference/controlFlowLoopAnalysis.errors.txt
@@ -0,0 +1,39 @@
+tests/cases/compiler/controlFlowLoopAnalysis.ts(13,25): error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+  Type 'undefined' is not assignable to type 'number'.
+
+
+==== tests/cases/compiler/controlFlowLoopAnalysis.ts (1 errors) ====
+    
+    // Repro from #8418
+    
+    let cond: boolean;
+    
+    function foo(x: number): number { return 1; }
+    
+    function test1() {
+        let x: number | undefined;
+        while (cond) {
+            while (cond) {
+                while (cond) {
+                    x = foo(x);
+                            ~
+!!! error TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
+!!! error TS2345:   Type 'undefined' is not assignable to type 'number'.
+                }
+            }
+            x = 1;
+        }
+    }
+    
+    // Repro from #8418
+    
+    function test2() {
+        let x: number | undefined;
+        x = 1;
+        while (cond) {
+            while (cond) {
+                x = foo(x);
+            }
+        }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/controlFlowLoopAnalysis.js b/tests/baselines/reference/controlFlowLoopAnalysis.js
new file mode 100644
index 00000000000..3cf2ce2caac
--- /dev/null
+++ b/tests/baselines/reference/controlFlowLoopAnalysis.js
@@ -0,0 +1,58 @@
+//// [controlFlowLoopAnalysis.ts]
+
+// Repro from #8418
+
+let cond: boolean;
+
+function foo(x: number): number { return 1; }
+
+function test1() {
+    let x: number | undefined;
+    while (cond) {
+        while (cond) {
+            while (cond) {
+                x = foo(x);
+            }
+        }
+        x = 1;
+    }
+}
+
+// Repro from #8418
+
+function test2() {
+    let x: number | undefined;
+    x = 1;
+    while (cond) {
+        while (cond) {
+            x = foo(x);
+        }
+    }
+}
+
+
+//// [controlFlowLoopAnalysis.js]
+// Repro from #8418
+var cond;
+function foo(x) { return 1; }
+function test1() {
+    var x;
+    while (cond) {
+        while (cond) {
+            while (cond) {
+                x = foo(x);
+            }
+        }
+        x = 1;
+    }
+}
+// Repro from #8418
+function test2() {
+    var x;
+    x = 1;
+    while (cond) {
+        while (cond) {
+            x = foo(x);
+        }
+    }
+}
diff --git a/tests/cases/compiler/controlFlowLoopAnalysis.ts b/tests/cases/compiler/controlFlowLoopAnalysis.ts
new file mode 100644
index 00000000000..60cb9436006
--- /dev/null
+++ b/tests/cases/compiler/controlFlowLoopAnalysis.ts
@@ -0,0 +1,31 @@
+// @strictNullChecks: true
+
+// Repro from #8418
+
+let cond: boolean;
+
+function foo(x: number): number { return 1; }
+
+function test1() {
+    let x: number | undefined;
+    while (cond) {
+        while (cond) {
+            while (cond) {
+                x = foo(x);
+            }
+        }
+        x = 1;
+    }
+}
+
+// Repro from #8418
+
+function test2() {
+    let x: number | undefined;
+    x = 1;
+    while (cond) {
+        while (cond) {
+            x = foo(x);
+        }
+    }
+}