diff --git a/clang/lib/Frontend/Rewrite/InclusionRewriter.cpp b/clang/lib/Frontend/Rewrite/InclusionRewriter.cpp
--- a/clang/lib/Frontend/Rewrite/InclusionRewriter.cpp
+++ b/clang/lib/Frontend/Rewrite/InclusionRewriter.cpp
@@ -281,27 +281,28 @@
 
   StringRef TextToWrite(FromFile.getBufferStart() + WriteFrom,
                         WriteTo - WriteFrom);
+  // count lines manually, it's faster than getPresumedLoc()
+  Line += TextToWrite.count(LocalEOL);
 
   if (MainEOL == LocalEOL) {
     OS << TextToWrite;
-    // count lines manually, it's faster than getPresumedLoc()
-    Line += TextToWrite.count(LocalEOL);
-    if (EnsureNewline && !TextToWrite.endswith(LocalEOL))
-      OS << MainEOL;
   } else {
     // Output the file one line at a time, rewriting the line endings as we go.
     StringRef Rest = TextToWrite;
     while (!Rest.empty()) {
-      StringRef LineText;
-      std::tie(LineText, Rest) = Rest.split(LocalEOL);
+      size_t Idx = Rest.find(LocalEOL);
+      StringRef LineText = Rest.substr(0, Idx);
       OS << LineText;
-      Line++;
-      if (!Rest.empty())
+      if (Idx != StringRef::npos) {
         OS << MainEOL;
+        Idx += LocalEOL.size();
+      }
+      Rest = Rest.substr(Idx);
     }
-    if (TextToWrite.endswith(LocalEOL) || EnsureNewline)
-      OS << MainEOL;
   }
+  if (EnsureNewline && !TextToWrite.endswith(LocalEOL))
+    OS << MainEOL;
+
   WriteFrom = WriteTo;
 }
 
diff --git a/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.h b/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.h
@@ -0,0 +1,11 @@
+// Note: This header file has CRLF line endings.
+// The indentation in some of the conditional inclusion directives below is
+// intentional and is required for this test to function as a regression test
+// for GH59736.
+_Static_assert(__LINE__ == 5, "");
+#if 1
+_Static_assert(__LINE__ == 7, "");
+  #if 1
+  _Static_assert(__LINE__ == 9, "");
+  #endif
+#endif
diff --git a/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.c b/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Frontend/rewrite-includes-mixed-eol-crlf.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -E -frewrite-includes %s | %clang_cc1 -
+// expected-no-diagnostics
+// Note: This source file has CRLF line endings.
+// This test validates that -frewrite-includes translates the end of line (EOL)
+// form used in header files to the EOL form used in the the primary source
+// file when the files use different EOL forms.
+#include "rewrite-includes-mixed-eol-crlf.h"
+#include "rewrite-includes-mixed-eol-lf.h"
diff --git a/clang/test/Frontend/rewrite-includes-mixed-eol-lf.h b/clang/test/Frontend/rewrite-includes-mixed-eol-lf.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Frontend/rewrite-includes-mixed-eol-lf.h
@@ -0,0 +1,11 @@
+// Note: This header file has LF line endings.
+// The indentation in some of the conditional inclusion directives below is
+// intentional and is required for this test to function as a regression test
+// for GH59736.
+_Static_assert(__LINE__ == 5, "");
+#if 1
+_Static_assert(__LINE__ == 7, "");
+  #if 1
+  _Static_assert(__LINE__ == 9, "");
+  #endif
+#endif
diff --git a/clang/test/Frontend/rewrite-includes-mixed-eol-lf.c b/clang/test/Frontend/rewrite-includes-mixed-eol-lf.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Frontend/rewrite-includes-mixed-eol-lf.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -E -frewrite-includes %s | %clang_cc1 -
+// expected-no-diagnostics
+// Note: This source file has LF line endings.
+// This test validates that -frewrite-includes translates the end of line (EOL)
+// form used in header files to the EOL form used in the the primary source
+// file when the files use different EOL forms.
+#include "rewrite-includes-mixed-eol-crlf.h"
+#include "rewrite-includes-mixed-eol-lf.h"