Index: include/llvm-c/lto.h
===================================================================
--- include/llvm-c/lto.h
+++ include/llvm-c/lto.h
@@ -784,7 +784,7 @@
 /**
  * Sets the cache pruning interval (in seconds). A negative value disables the
  * pruning. An unspecified default value will be applied, and a value of 0 will
- * be ignored.
+ * be force prunning to occur.
  *
  * \since LTO_API_VERSION=18
  */
Index: include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
===================================================================
--- include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -131,7 +131,8 @@
    * To avoid filling the disk space, a few knobs are provided:
    *  - The pruning interval limit the frequency at which the garbage collector
    *    will try to scan the cache directory to prune it from expired entries.
-   *    Setting to -1 disable the pruning (default).
+   *    Setting to -1 disable the pruning (default). Setting to 0 force pruning
+   *    to occur.
    *  - The pruning expiration time indicates to the garbage collector how old
    *    an entry needs to be to be removed.
    *  - Finally, the garbage collector can be instructed to prune the cache till
@@ -149,10 +150,9 @@
   void setCacheDir(std::string Path) { CacheOptions.Path = std::move(Path); }
 
   /// Cache policy: interval (seconds) between two prunes of the cache. Set to a
-  /// negative value to disable pruning. A value of 0 will be ignored.
+  /// negative value to disable pruning. A value of 0 will force prunning to
+  /// occur.
   void setCachePruningInterval(int Interval) {
-    if (Interval == 0)
-      return;
     if(Interval < 0)
       CacheOptions.Policy.Interval.reset();
     else
Index: test/ThinLTO/X86/cache.ll
===================================================================
--- test/ThinLTO/X86/cache.ll
+++ test/ThinLTO/X86/cache.ll
@@ -59,6 +59,27 @@
 ; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache --thinlto-cache-pruning-interval -1
 ; RUN: ls %t.cache/llvmcache-foo
 
+; Verify that the pruner doesn't run and a cache file is not deleted when: 
+; default values for pruning interval and cache expiration are used, 
+; llvmcache.timestamp is current, 
+; cache file is older than default cache expiration value.
+; RUN: rm -Rf %t.cache && mkdir %t.cache
+; RUN: touch -t 197001011200 %t.cache/llvmcache-foo
+; RUN: touch %t.cache/llvmcache.timestamp
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache
+; RUN: ls %t.cache/llvmcache-foo
+
+; Verify that the pruner runs and a cache file is deleted when:
+; pruning interval has value 0 (i.e. run garbage collector now)
+; default value for cache expiration is used,
+; llvmcache.timestamp is current,
+; cache file is older than default cache expiration value.
+; RUN: rm -Rf %t.cache && mkdir %t.cache
+; RUN: touch -t 197001011200 %t.cache/llvmcache-foo
+; RUN: touch %t.cache/llvmcache.timestamp
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache --thinlto-cache-pruning-interval 0
+; RUN: not ls %t.cache/llvmcache-foo
+
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.11.0"
 
Index: tools/llvm-lto/llvm-lto.cpp
===================================================================
--- tools/llvm-lto/llvm-lto.cpp
+++ tools/llvm-lto/llvm-lto.cpp
@@ -157,7 +157,8 @@
     ThinLTOCacheDir("thinlto-cache-dir", cl::desc("Enable ThinLTO caching."));
 
 static cl::opt<int>
-    ThinLTOCachePruningInterval("thinlto-cache-pruning-interval", cl::desc("Set ThinLTO cache pruning interval."));
+    ThinLTOCachePruningInterval("thinlto-cache-pruning-interval", 
+    cl::init(1200), cl::desc("Set ThinLTO cache pruning interval."));
 
 static cl::opt<std::string> ThinLTOSaveTempsPrefix(
     "thinlto-save-temps",