diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 00ddb416e2263..739c82287254d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4409,7 +4409,7 @@ namespace ts {
                 const special = getSpecialPropertyAssignmentKind(expression);
                 if (special === SpecialPropertyAssignmentKind.ThisProperty) {
                     const thisContainer = getThisContainer(expression, /*includeArrowFunctions*/ false);
-                    // Properties defined in a constructor (or javascript constructor function) don't get undefined added.
+                    // Properties defined in a constructor (or base constructor, or javascript constructor function) don't get undefined added.
                     // Function expressions that are assigned to the prototype count as methods.
                     declarationInConstructor = thisContainer.kind === SyntaxKind.Constructor ||
                         thisContainer.kind === SyntaxKind.FunctionDeclaration ||
@@ -4479,7 +4479,14 @@ namespace ts {
             }
             let type = jsDocType;
             if (!type) {
-                // use only the constructor types unless only null | undefined (including widening variants) were assigned there
+                // use only the constructor types unless they were only assigned null | undefined (including widening variants)
+                if (definedInMethod) {
+                    const propType = getTypeOfSpecialPropertyOfBaseType(symbol);
+                    if (propType) {
+                        (constructorTypes || (constructorTypes = [])).push(propType);
+                        definedInConstructor = true;
+                    }
+                }
                 const sourceTypes = some(constructorTypes, t => !!(t.flags & ~(TypeFlags.Nullable | TypeFlags.ContainsWideningType))) ? constructorTypes : types;
                 type = getUnionType(sourceTypes, UnionReduction.Subtype);
             }
@@ -4493,6 +4500,20 @@ namespace ts {
             return widened;
         }
 
+        /** check for definition in base class if any declaration is in a class */
+        function getTypeOfSpecialPropertyOfBaseType(specialProperty: Symbol) {
+            const parentDeclaration = forEach(specialProperty.declarations, d => {
+                const parent = getThisContainer(d, /*includeArrowFunctions*/ false).parent;
+                return isClassLike(parent) && parent;
+            });
+            if (parentDeclaration) {
+                const classType = getDeclaredTypeOfSymbol(getSymbolOfNode(parentDeclaration)) as InterfaceType;
+                const baseClassType = classType && getBaseTypes(classType)[0];
+                if (baseClassType) {
+                    return getTypeOfPropertyOfType(baseClassType, specialProperty.escapedName);
+                }
+            }
+        }
 
         // Return the type implied by a binding pattern element. This is the type of the initializer of the element if
         // one is present. Otherwise, if the element is itself a binding pattern, it is the type implied by the binding
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments3.symbols b/tests/baselines/reference/inferringClassMembersFromAssignments3.symbols
new file mode 100644
index 0000000000000..b4006600dbe58
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments3.symbols
@@ -0,0 +1,25 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    constructor() {
+        this.p = 1
+>this.p : Symbol(Base.p, Decl(a.js, 1, 19))
+>this : Symbol(Base, Decl(a.js, 0, 0))
+>p : Symbol(Base.p, Decl(a.js, 1, 19))
+    }
+}
+class Derived extends Base {
+>Derived : Symbol(Derived, Decl(a.js, 4, 1))
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    m() {
+>m : Symbol(Derived.m, Decl(a.js, 5, 28))
+
+        this.p = 1
+>this.p : Symbol(Derived.p, Decl(a.js, 6, 9))
+>this : Symbol(Derived, Decl(a.js, 4, 1))
+>p : Symbol(Derived.p, Decl(a.js, 6, 9))
+    }
+}
+
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments3.types b/tests/baselines/reference/inferringClassMembersFromAssignments3.types
new file mode 100644
index 0000000000000..60d545b2832fe
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments3.types
@@ -0,0 +1,29 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Base
+
+    constructor() {
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number
+>this : this
+>p : number
+>1 : 1
+    }
+}
+class Derived extends Base {
+>Derived : Derived
+>Base : Base
+
+    m() {
+>m : () => void
+
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number
+>this : this
+>p : number
+>1 : 1
+    }
+}
+
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments4.symbols b/tests/baselines/reference/inferringClassMembersFromAssignments4.symbols
new file mode 100644
index 0000000000000..d0d438c3ed381
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments4.symbols
@@ -0,0 +1,28 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    m() {
+>m : Symbol(Base.m, Decl(a.js, 0, 12))
+
+        this.p = 1
+>this.p : Symbol(Base.p, Decl(a.js, 1, 9))
+>this : Symbol(Base, Decl(a.js, 0, 0))
+>p : Symbol(Base.p, Decl(a.js, 1, 9))
+    }
+}
+class Derived extends Base {
+>Derived : Symbol(Derived, Decl(a.js, 4, 1))
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    m() {
+>m : Symbol(Derived.m, Decl(a.js, 5, 28))
+
+        // should be OK, and p should have type number | undefined from its base
+        this.p = 1
+>this.p : Symbol(Derived.p, Decl(a.js, 6, 9))
+>this : Symbol(Derived, Decl(a.js, 4, 1))
+>p : Symbol(Derived.p, Decl(a.js, 6, 9))
+    }
+}
+
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments4.types b/tests/baselines/reference/inferringClassMembersFromAssignments4.types
new file mode 100644
index 0000000000000..f20602d188e7d
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments4.types
@@ -0,0 +1,32 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Base
+
+    m() {
+>m : () => void
+
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number | undefined
+>this : this
+>p : number | undefined
+>1 : 1
+    }
+}
+class Derived extends Base {
+>Derived : Derived
+>Base : Base
+
+    m() {
+>m : () => void
+
+        // should be OK, and p should have type number | undefined from its base
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number | undefined
+>this : this
+>p : number | undefined
+>1 : 1
+    }
+}
+
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments5.symbols b/tests/baselines/reference/inferringClassMembersFromAssignments5.symbols
new file mode 100644
index 0000000000000..5c46300d77009
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments5.symbols
@@ -0,0 +1,37 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    m() {
+>m : Symbol(Base.m, Decl(a.js, 0, 12))
+
+        this.p = 1
+>this.p : Symbol(Base.p, Decl(a.js, 1, 9))
+>this : Symbol(Base, Decl(a.js, 0, 0))
+>p : Symbol(Base.p, Decl(a.js, 1, 9))
+    }
+}
+class Derived extends Base {
+>Derived : Symbol(Derived, Decl(a.js, 4, 1))
+>Base : Symbol(Base, Decl(a.js, 0, 0))
+
+    constructor() {
+        super();
+>super : Symbol(Base, Decl(a.js, 0, 0))
+
+        // should be OK, and p should have type number from this assignment
+        this.p = 1
+>this.p : Symbol(Derived.p, Decl(a.js, 7, 16))
+>this : Symbol(Derived, Decl(a.js, 4, 1))
+>p : Symbol(Derived.p, Decl(a.js, 7, 16))
+    }
+    test() {
+>test : Symbol(Derived.test, Decl(a.js, 10, 5))
+
+        return this.p
+>this.p : Symbol(Derived.p, Decl(a.js, 7, 16))
+>this : Symbol(Derived, Decl(a.js, 4, 1))
+>p : Symbol(Derived.p, Decl(a.js, 7, 16))
+    }
+}
+
diff --git a/tests/baselines/reference/inferringClassMembersFromAssignments5.types b/tests/baselines/reference/inferringClassMembersFromAssignments5.types
new file mode 100644
index 0000000000000..fc95b82e5fdeb
--- /dev/null
+++ b/tests/baselines/reference/inferringClassMembersFromAssignments5.types
@@ -0,0 +1,42 @@
+=== tests/cases/conformance/salsa/a.js ===
+class Base {
+>Base : Base
+
+    m() {
+>m : () => void
+
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number | undefined
+>this : this
+>p : number | undefined
+>1 : 1
+    }
+}
+class Derived extends Base {
+>Derived : Derived
+>Base : Base
+
+    constructor() {
+        super();
+>super() : void
+>super : typeof Base
+
+        // should be OK, and p should have type number from this assignment
+        this.p = 1
+>this.p = 1 : 1
+>this.p : number
+>this : this
+>p : number
+>1 : 1
+    }
+    test() {
+>test : () => number
+
+        return this.p
+>this.p : number
+>this : this
+>p : number
+    }
+}
+
diff --git a/tests/cases/conformance/salsa/inferringClassMembersFromAssignments3.ts b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments3.ts
new file mode 100644
index 0000000000000..800bd368dba40
--- /dev/null
+++ b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments3.ts
@@ -0,0 +1,16 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @noImplicitAny: true
+// @strictNullChecks: true
+// @Filename: a.js
+class Base {
+    constructor() {
+        this.p = 1
+    }
+}
+class Derived extends Base {
+    m() {
+        this.p = 1
+    }
+}
diff --git a/tests/cases/conformance/salsa/inferringClassMembersFromAssignments4.ts b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments4.ts
new file mode 100644
index 0000000000000..ba443bf859541
--- /dev/null
+++ b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments4.ts
@@ -0,0 +1,17 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @noImplicitAny: true
+// @strictNullChecks: true
+// @Filename: a.js
+class Base {
+    m() {
+        this.p = 1
+    }
+}
+class Derived extends Base {
+    m() {
+        // should be OK, and p should have type number | undefined from its base
+        this.p = 1
+    }
+}
diff --git a/tests/cases/conformance/salsa/inferringClassMembersFromAssignments5.ts b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments5.ts
new file mode 100644
index 0000000000000..5044ea396eb4f
--- /dev/null
+++ b/tests/cases/conformance/salsa/inferringClassMembersFromAssignments5.ts
@@ -0,0 +1,21 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @noImplicitAny: true
+// @strictNullChecks: true
+// @Filename: a.js
+class Base {
+    m() {
+        this.p = 1
+    }
+}
+class Derived extends Base {
+    constructor() {
+        super();
+        // should be OK, and p should have type number from this assignment
+        this.p = 1
+    }
+    test() {
+        return this.p
+    }
+}