diff --git a/var/spack/repos/builtin/packages/llvm/package.py b/var/spack/repos/builtin/packages/llvm/package.py
index 14433c1aa1..1f9f4c8313 100644
--- a/var/spack/repos/builtin/packages/llvm/package.py
+++ b/var/spack/repos/builtin/packages/llvm/package.py
@@ -499,7 +499,16 @@ def cmake_args(self):
             cmake_args.append("-DLIBOMP_TSAN_SUPPORT=ON")
 
         if self.compiler.name == "gcc":
-            gcc_prefix = ancestor(self.compiler.cc, 2)
+            compiler = Executable(self.compiler.cc)
+            gcc_output = compiler('-print-search-dirs', output=str, error=str)
+
+            for line in gcc_output.splitlines():
+                if line.startswith("install:"):
+                    # Get path and strip any whitespace
+                    # (causes oddity with ancestor)
+                    gcc_prefix = line.split(":")[1].strip()
+                    gcc_prefix = ancestor(gcc_prefix, 4)
+                    break
             cmake_args.append("-DGCC_INSTALL_PREFIX=" + gcc_prefix)
 
         if spec.satisfies("@4.0.0:"):