Index: include/llvm/DebugInfo/MSF/MSFCommon.h
===================================================================
--- include/llvm/DebugInfo/MSF/MSFCommon.h
+++ include/llvm/DebugInfo/MSF/MSFCommon.h
@@ -110,12 +110,15 @@
 
 inline uint32_t getNumFpmIntervals(const MSFLayout &L,
                                    bool IncludeUnusedFpmData = false) {
+  // Need to subtract the free block map index from the number of blocks
+  // so the blocks before Fpm (SB & Fpm0 if using Fpm1) aren't included
+  // Need to add 1 to block size so the interval includes the already present FPM blocks
   if (IncludeUnusedFpmData)
-    return divideCeil(L.SB->NumBlocks, L.SB->BlockSize);
+    return divideCeil(L.SB->NumBlocks - L.SB->FreeBlockMapBlock, L.SB->BlockSize + 1);
 
   // We want the minimum number of intervals required, where each interval can
   // represent BlockSize * 8 blocks.
-  return divideCeil(L.SB->NumBlocks, 8 * L.SB->BlockSize);
+  return divideCeil(L.SB->NumBlocks - L.SB->FreeBlockMapBlock, 8 * L.SB->BlockSize);
 }
 
 Error validateSuperBlock(const SuperBlock &SB);