Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp
+++ lib/Format/Format.cpp
@@ -559,7 +559,7 @@
       Limit -= 2;
 
       unsigned MergedLines = 0;
-      if (MergeShortFunctions) {
+      if (MergeShortFunctions && TheLine->MustBeDeclaration) {
         MergedLines = tryMergeSimpleBlock(I + 1, E, Limit);
         // If we managed to merge the block, count the function header, which is
         // on a separate line.
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -7336,6 +7336,26 @@
                "}\n"
                "}",
                BreakBeforeBrace);
+
+  verifyFormat("#ifdef _DEBUG\n"
+               "int foo(int i = 0)\n"
+               "#else\n"
+               "int foo(int i = 5)\n"
+               "#endif\n"
+               "{\n"
+               "  return i;\n"
+               "}\n"
+               "void foo1()\n"
+               "#ifdef _DEBUG\n"
+               "{\n"
+               "  return 0;\n"
+               "}\n"
+               "#else\n"
+               "{\n"
+               "  return 5;\n"
+               "}\n"
+               "#endif",
+               BreakBeforeBrace);
 }
 
 TEST_F(FormatTest, AllmanBraceBreaking) {
@@ -7418,6 +7438,26 @@
                "}\n",
                BreakBeforeBrace);
 
+  verifyFormat("#ifdef _DEBUG\n"
+               "int foo(int i = 0)\n"
+               "#else\n"
+               "int foo(int i = 5)\n"
+               "#endif\n"
+               "{\n"
+               "  return i;\n"
+               "}\n"
+               "void foo1()\n"
+               "#ifdef _DEBUG\n"
+               "{\n"
+               "  return 0;\n"
+               "}\n"
+               "#else\n"
+               "{\n"
+               "  return 5;\n"
+               "}\n"
+               "#endif",
+               BreakBeforeBrace);
+
   BreakBeforeBrace.ColumnLimit = 19;
   verifyFormat("void f() { int i; }", BreakBeforeBrace);
   BreakBeforeBrace.ColumnLimit = 18;
@@ -7538,6 +7578,26 @@
                "  Y = 0,\n"
                "}\n",
                GNUBraceStyle);
+
+  verifyFormat("#ifdef _DEBUG\n"
+               "int foo(int i = 0)\n"
+               "#else\n"
+               "int foo(int i = 5)\n"
+               "#endif\n"
+               "{\n"
+               "  return i;\n"
+               "}\n"
+               "void foo1()\n"
+               "#ifdef _DEBUG\n"
+               "{\n"
+               "  return 0;\n"
+               "}\n"
+               "#else\n"
+               "{\n"
+               "  return 5;\n"
+               "}\n"
+               "#endif",
+               GNUBraceStyle);
 }
 TEST_F(FormatTest, CatchExceptionReferenceBinding) {
   verifyFormat("void f() {\n"