diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/Makefile b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/Makefile
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/Makefile
@@ -0,0 +1,3 @@
+CXX_SOURCES   := main.cpp module1.cpp module2.cpp base_module.cpp
+
+include Makefile.rules
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/TestTemplateWithSameArg.py b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/TestTemplateWithSameArg.py
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/TestTemplateWithSameArg.py
@@ -0,0 +1,72 @@
+"""
+Tests the scenario where we evaluate expressions
+of two types in different modules that reference
+a class template instantiated with the same
+template argument.
+
+Note that,
+1. Since the decls originate from modules, LLDB
+   marks them as such and Clang doesn't create
+   a LookupPtr map on the corresponding DeclContext.
+   This prevents regular DeclContext::lookup from
+   succeeding.
+2. Because we reference the same class template
+   from two different modules we get a redeclaration
+   chain for the class's ClassTemplateSpecializationDecl.
+   The importer will import all FieldDecls into the
+   same DeclContext on the redeclaration chain. If
+   we don't do the bookkeeping correctly we end up
+   with duplicate decls on the same DeclContext leading
+   to crashes down the line.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestTemplateWithSameArg(TestBase):
+
+    def setUp(self):
+        TestBase.setUp(self)
+        self.build()
+        self.main_source_file = lldb.SBFileSpec("main.cpp")
+
+    @add_test_categories(["gmodules"])
+    @skipIf(bugnumber='rdar://96581048')
+    def test_same_template_arg(self):
+        lldbutil.run_to_source_breakpoint(self, "Break here", self.main_source_file)
+
+        self.expect_expr("FromMod1", result_type="ClassInMod1", result_children=[
+                ValueCheck(name="VecInMod1", children=[
+                            ValueCheck(name="Member", value="137")
+                    ])
+            ])
+
+        self.expect_expr("FromMod2", result_type="ClassInMod2", result_children=[
+                ValueCheck(name="VecInMod2", children=[
+                            ValueCheck(name="Member", value="42")
+                    ])
+            ])
+
+    @add_test_categories(["gmodules"])
+    @skipIf(bugnumber='rdar://96581048')
+    def test_duplicate_decls(self):
+        lldbutil.run_to_source_breakpoint(self, "Break here", self.main_source_file)
+
+        self.expect_expr("(intptr_t)&FromMod1 + (intptr_t)&FromMod2")
+
+        # Make sure we only have a single 'Member' decl on the AST
+        self.filecheck("target module dump ast", __file__)
+# CHECK:      ClassTemplateSpecializationDecl {{.*}} imported in Module2 struct ClassInMod3 definition
+# CHECK-NEXT: |-DefinitionData pass_in_registers aggregate standard_layout trivially_copyable pod trivial
+# CHECK-NEXT: | |-DefaultConstructor exists trivial needs_implicit
+# CHECK-NEXT: | |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
+# CHECK-NEXT: | |-MoveConstructor exists simple trivial needs_implicit
+# CHECK-NEXT: | |-CopyAssignment simple trivial has_const_param needs_implicit implicit_has_const_param
+# CHECK-NEXT: | |-MoveAssignment exists simple trivial needs_implicit
+# CHECK-NEXT: | `-Destructor simple irrelevant trivial needs_implicit
+# CHECK-NEXT: |-TemplateArgument type 'int'
+# CHECK-NEXT: | `-BuiltinType {{.*}} 'int'
+# CHECK-NEXT: `-FieldDecl {{.*}} imported in Module2 Member 'int'
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.h b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.h
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.h
@@ -0,0 +1,6 @@
+#ifndef MOD3_H_IN
+#define MOD3_H_IN
+
+template <typename SIZE_T> struct ClassInMod3 { int Member = 0; };
+
+#endif // _H_IN
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.cpp b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/base_module.cpp
@@ -0,0 +1,3 @@
+#include "base_module.h"
+
+namespace crash {} // namespace crash
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/main.cpp b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/main.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/main.cpp
@@ -0,0 +1,15 @@
+#include "module1.h"
+#include "module2.h"
+
+#include <cstdio>
+
+int main() {
+  ClassInMod1 FromMod1;
+  ClassInMod2 FromMod2;
+
+  FromMod1.VecInMod1.Member = 137;
+  FromMod2.VecInMod2.Member = 42;
+
+  std::puts("Break here");
+  return 0;
+}
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module.modulemap b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module.modulemap
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module.modulemap
@@ -0,0 +1,14 @@
+module Module1 {
+  header "module1.h"
+  export *
+}
+
+module Module2 {
+  header "module2.h"
+  export *
+}
+
+module BaseModule {
+  header "base_module.h"
+  export *
+}
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.h b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.h
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.h
@@ -0,0 +1,10 @@
+#ifndef MOD1_H_IN
+#define MOD1_H_IN
+
+#include "base_module.h"
+
+struct ClassInMod1 {
+  ClassInMod3<int> VecInMod1;
+};
+
+#endif // _H_IN
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.cpp b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module1.cpp
@@ -0,0 +1,3 @@
+#include "module1.h"
+
+namespace crash {} // namespace crash
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.h b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.h
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.h
@@ -0,0 +1,10 @@
+#ifndef MOD2_H_IN
+#define MOD2_H_IN
+
+#include "base_module.h"
+
+struct ClassInMod2 {
+  ClassInMod3<int> VecInMod2;
+};
+
+#endif
diff --git a/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.cpp b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/lang/cpp/gmodules/template-with-same-arg/module2.cpp
@@ -0,0 +1,3 @@
+#include "module2.h"
+
+namespace crash {} // namespace crash