diff --git a/src/compiler/factory.ts b/src/compiler/factory.ts
index d5d8482a0ba..5f94ae8931a 100644
--- a/src/compiler/factory.ts
+++ b/src/compiler/factory.ts
@@ -2599,7 +2599,6 @@ namespace ts {
      * @param visitor: Optional callback used to visit any custom prologue directives.
      */
     export function addPrologueDirectives(target: Statement[], source: Statement[], ensureUseStrict?: boolean, visitor?: (node: Node) => VisitResult<Node>): number {
-        Debug.assert(target.length === 0, "Prologue directives should be at the first statement in the target statements array");
         let foundUseStrict = false;
         let statementOffset = 0;
         const numStatements = source.length;
diff --git a/src/compiler/transformers/es2015.ts b/src/compiler/transformers/es2015.ts
index e0fd435a90d..8353e393aa4 100644
--- a/src/compiler/transformers/es2015.ts
+++ b/src/compiler/transformers/es2015.ts
@@ -507,8 +507,8 @@ namespace ts {
             const ancestorFacts = enterSubtree(HierarchyFacts.SourceFileExcludes, HierarchyFacts.SourceFileIncludes);
             const statements: Statement[] = [];
             startLexicalEnvironment();
-            const statementOffset = addPrologueDirectives(statements, node.statements, /*ensureUseStrict*/ false, visitor);
             addCaptureThisForNodeIfNeeded(statements, node);
+            const statementOffset = addPrologueDirectives(statements, node.statements, /*ensureUseStrict*/ false, visitor);
             addRange(statements, visitNodes(node.statements, visitor, isStatement, statementOffset));
             addRange(statements, endLexicalEnvironment());
             exitSubtree(ancestorFacts, HierarchyFacts.None, HierarchyFacts.None);
@@ -915,14 +915,14 @@ namespace ts {
                 // The assumption is that no prior step in the pipeline has added any prologue directives.
                 statementOffset = 0;
             }
-            else if (constructor) {
-                // Otherwise, try to emit all potential prologue directives first.
-                statementOffset = addPrologueDirectives(statements, constructor.body.statements, /*ensureUseStrict*/ false, visitor);
-            }
 
             if (constructor) {
                 addDefaultValueAssignmentsIfNeeded(statements, constructor);
                 addRestParameterIfNeeded(statements, constructor, hasSynthesizedSuper);
+                if (!hasSynthesizedSuper) {
+                    // If no super call has been synthesized, try to emit all potential prologue directives.
+                    statementOffset = addPrologueDirectives(statements, constructor.body.statements, /*ensureUseStrict*/ false, visitor);
+                }
                 Debug.assert(statementOffset >= 0, "statementOffset not initialized correctly!");
 
             }
@@ -1806,15 +1806,8 @@ namespace ts {
 
             const statements: Statement[] = [];
             const body = node.body;
-            let statementOffset: number;
 
             resumeLexicalEnvironment();
-            if (isBlock(body)) {
-                // ensureUseStrict is false because no new prologue-directive should be added.
-                // addPrologueDirectives will simply put already-existing directives at the beginning of the target statement-array
-                statementOffset = addPrologueDirectives(statements, body.statements, /*ensureUseStrict*/ false, visitor);
-            }
-
             addCaptureThisForNodeIfNeeded(statements, node);
             addDefaultValueAssignmentsIfNeeded(statements, node);
             addRestParameterIfNeeded(statements, node, /*inConstructorWithSynthesizedSuper*/ false);
@@ -1825,6 +1818,10 @@ namespace ts {
             }
 
             if (isBlock(body)) {
+                // ensureUseStrict is false because no new prologue-directive should be added.
+                // addPrologueDirectives will simply put already-existing directives at the beginning of the target statement-array
+                const statementOffset = addPrologueDirectives(statements, body.statements, /*ensureUseStrict*/ false, visitor);
+
                 statementsLocation = body.statements;
                 addRange(statements, visitNodes(body.statements, visitor, isStatement, statementOffset));
 
diff --git a/src/compiler/transformers/esnext.ts b/src/compiler/transformers/esnext.ts
index c413415380d..f058e627df7 100644
--- a/src/compiler/transformers/esnext.ts
+++ b/src/compiler/transformers/esnext.ts
@@ -375,6 +375,7 @@ namespace ts {
                                 declarations
                             )
                         );
+                        setEmitFlags(statement, EmitFlags.CustomPrologue);
                         leadingStatements = append(leadingStatements, statement);
                     }
                 }