diff --git a/lib/DebugInfo/MSF/MSFCommon.cpp b/lib/DebugInfo/MSF/MSFCommon.cpp
index d79ccafe898..fdab7884646 100644
--- a/lib/DebugInfo/MSF/MSFCommon.cpp
+++ b/lib/DebugInfo/MSF/MSFCommon.cpp
@@ -44,5 +44,14 @@ Error llvm::msf::validateSuperBlock(const SuperBlock &SB) {
     return make_error<MSFError>(msf_error_code::invalid_format,
                                 "Block 0 is reserved");
 
+  if (SB.BlockMapAddr >= SB.NumBlocks)
+    return make_error<MSFError>(msf_error_code::invalid_format,
+                                "Block map address is invalid.");
+
+  if (SB.FreeBlockMapBlock != 1 && SB.FreeBlockMapBlock != 2)
+    return make_error<MSFError>(
+        msf_error_code::invalid_format,
+        "The free block map isn't at block 1 or block 2.");
+
   return Error::success();
 }
diff --git a/unittests/DebugInfo/PDB/MSFBuilderTest.cpp b/unittests/DebugInfo/PDB/MSFBuilderTest.cpp
index bc1ec522fb4..5f2f0c271e9 100644
--- a/unittests/DebugInfo/PDB/MSFBuilderTest.cpp
+++ b/unittests/DebugInfo/PDB/MSFBuilderTest.cpp
@@ -30,6 +30,7 @@ protected:
     ::memset(&SB, 0, sizeof(SB));
 
     ::memcpy(SB.MagicBytes, msf::Magic, sizeof(msf::Magic));
+    SB.FreeBlockMapBlock = 1;
     SB.BlockMapAddr = 1;
     SB.BlockSize = 4096;
     SB.NumDirectoryBytes = 0;