diff --git a/lib/IRGen/GenDecl.cpp b/lib/IRGen/GenDecl.cpp
index d50173195d07e..f79cec8c594e2 100644
--- a/lib/IRGen/GenDecl.cpp
+++ b/lib/IRGen/GenDecl.cpp
@@ -1105,8 +1105,11 @@ void IRGenerator::emitGlobalTopLevel(llvm::StringSet<> *linkerDirectives) {
     IGM->emitSILDifferentiabilityWitness(&dw);
   }
 
-  // Emit code coverage mapping data.
-  PrimaryIGM->emitCoverageMapping();
+  // Emit code coverage mapping data for all modules
+  for (auto Iter : *this) {
+    IRGenModule *IGM = Iter.second;
+    IGM->emitCoverageMapping();
+  }
 
   for (auto Iter : *this) {
     IRGenModule *IGM = Iter.second;
diff --git a/test/Profiler/Inputs/coverage_num_threads1.swift b/test/Profiler/Inputs/coverage_num_threads1.swift
new file mode 100644
index 0000000000000..6ca641732e7e1
--- /dev/null
+++ b/test/Profiler/Inputs/coverage_num_threads1.swift
@@ -0,0 +1 @@
+func func1() {}
diff --git a/test/Profiler/Inputs/coverage_num_threads2.swift b/test/Profiler/Inputs/coverage_num_threads2.swift
new file mode 100644
index 0000000000000..639ea1b4ad4b7
--- /dev/null
+++ b/test/Profiler/Inputs/coverage_num_threads2.swift
@@ -0,0 +1 @@
+func func2() {}
diff --git a/test/Profiler/coverage_num_threads.swift b/test/Profiler/coverage_num_threads.swift
new file mode 100644
index 0000000000000..12156483c079e
--- /dev/null
+++ b/test/Profiler/coverage_num_threads.swift
@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 0 -emit-ir %S/Inputs/coverage_num_threads1.swift | %FileCheck %s -check-prefix=SINGLE-SOURCE --implicit-check-not="llvm_coverage_mapping ="
+
+// SINGLE-SOURCE: llvm_coverage_mapping =
+
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 0 -emit-ir %S/Inputs/coverage_num_threads1.swift %S/Inputs/coverage_num_threads2.swift | %FileCheck %s -check-prefix=SINGLE-OBJECT --implicit-check-not="llvm_coverage_mapping ="
+
+// SINGLE-OBJECT: llvm_coverage_mapping =
+
+// Using 1 goes down the multithreaded codepath but only operates with a single thread to work around an issue on Windows where the output of both IR modules is interleaved and therefore the output is invalid
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 1 -emit-ir %S/Inputs/coverage_num_threads1.swift %S/Inputs/coverage_num_threads2.swift | %FileCheck %s -check-prefix=MULTIPLE-OBJECTS --implicit-check-not="llvm_coverage_mapping ="
+
+// MULTIPLE-OBJECTS: llvm_coverage_mapping =
+// MULTIPLE-OBJECTS: llvm_coverage_mapping =