diff --git a/lib/spack/spack/compiler.py b/lib/spack/spack/compiler.py
index 70da3ca2c42..72b2a340fd3 100644
--- a/lib/spack/spack/compiler.py
+++ b/lib/spack/spack/compiler.py
@@ -334,6 +334,40 @@ def __init__(
         # used for version checks for API, e.g. C++11 flag
         self._real_version = None
 
+    def __eq__(self, other):
+        return (
+            self.cc == other.cc
+            and self.cxx == other.cxx
+            and self.fc == other.fc
+            and self.f77 == other.f77
+            and self.spec == other.spec
+            and self.operating_system == other.operating_system
+            and self.target == other.target
+            and self.flags == other.flags
+            and self.modules == other.modules
+            and self.environment == other.environment
+            and self.extra_rpaths == other.extra_rpaths
+            and self.enable_implicit_rpaths == other.enable_implicit_rpaths
+        )
+
+    def __hash__(self):
+        return hash(
+            (
+                self.cc,
+                self.cxx,
+                self.fc,
+                self.f77,
+                self.spec,
+                self.operating_system,
+                self.target,
+                str(self.flags),
+                str(self.modules),
+                str(self.environment),
+                str(self.extra_rpaths),
+                self.enable_implicit_rpaths,
+            )
+        )
+
     def verify_executables(self):
         """Raise an error if any of the compiler executables is not valid.
 
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index 67438aaf38d..c089164aade 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -208,7 +208,7 @@ def _compiler_config_from_external(config):
             "modules": config.get("modules", []),
             "environment": extra_attributes.get("environment", {}),
             "extra_rpaths": extra_attributes.get("extra_rpaths", []),
-            "implicit_rpaths": extra_attributes.get("implicit_rpaths", True),
+            "implicit_rpaths": extra_attributes.get("implicit_rpaths", None),
         }
     }
     return compiler_entry
@@ -315,7 +315,9 @@ def all_compilers_config(scope=None, init_config=True):
     """
     from_compilers_yaml = get_compiler_config(scope, init_config)
     from_packages_yaml = get_compiler_config_from_packages(scope)
-    return from_compilers_yaml + from_packages_yaml
+    result = from_compilers_yaml + from_packages_yaml
+    key = lambda c: _compiler_from_config_entry(c["compiler"])
+    return list(llnl.util.lang.dedupe(result, key=key))
 
 
 def all_compiler_specs(scope=None, init_config=True):