diff --git a/azure-pipelines/e2e-ports/duplicate-file-a/portfile.cmake b/azure-pipelines/e2e-ports/duplicate-file-a/portfile.cmake
new file mode 100644
index 0000000000..98d000daaf
--- /dev/null
+++ b/azure-pipelines/e2e-ports/duplicate-file-a/portfile.cmake
@@ -0,0 +1,4 @@
+set(VCPKG_BUILD_TYPE release)
+
+file(MAKE_DIRECTORY "${CURRENT_PACKAGES_DIR}/include/")
+file(WRITE "${CURRENT_PACKAGES_DIR}/include/COMMON.H" "// THIS IS A HEADER FILE")
diff --git a/azure-pipelines/e2e-ports/duplicate-file-a/vcpkg.json b/azure-pipelines/e2e-ports/duplicate-file-a/vcpkg.json
new file mode 100644
index 0000000000..55fb068b2a
--- /dev/null
+++ b/azure-pipelines/e2e-ports/duplicate-file-a/vcpkg.json
@@ -0,0 +1,4 @@
+{
+  "name": "duplicate-file-a",
+  "version": "0.0.1"
+}
diff --git a/azure-pipelines/e2e-ports/duplicate-file-b/portfile.cmake b/azure-pipelines/e2e-ports/duplicate-file-b/portfile.cmake
new file mode 100644
index 0000000000..c82628c96b
--- /dev/null
+++ b/azure-pipelines/e2e-ports/duplicate-file-b/portfile.cmake
@@ -0,0 +1,4 @@
+set(VCPKG_BUILD_TYPE release)
+
+file(MAKE_DIRECTORY "${CURRENT_PACKAGES_DIR}/include/")
+file(WRITE "${CURRENT_PACKAGES_DIR}/include/common.h" "// THIS IS A HEADER FILE")
diff --git a/azure-pipelines/e2e-ports/duplicate-file-b/vcpkg.json b/azure-pipelines/e2e-ports/duplicate-file-b/vcpkg.json
new file mode 100644
index 0000000000..ae41528023
--- /dev/null
+++ b/azure-pipelines/e2e-ports/duplicate-file-b/vcpkg.json
@@ -0,0 +1,4 @@
+{
+  "name": "duplicate-file-b",
+  "version": "0.0.1"
+}
diff --git a/azure-pipelines/end-to-end-tests-dir/post-build-checks.ps1 b/azure-pipelines/end-to-end-tests-dir/post-build-checks.ps1
index 2ae56da212..2ce8fac406 100644
--- a/azure-pipelines/end-to-end-tests-dir/post-build-checks.ps1
+++ b/azure-pipelines/end-to-end-tests-dir/post-build-checks.ps1
@@ -5,6 +5,14 @@ if ($IsWindows) {
     $NativeSlash = '\'
 }
 
+# Fail if installed files exist
+Refresh-TestRoot
+[string]$dupOutput = Run-VcpkgAndCaptureOutput install @commonArgs "--overlay-ports=$PSScriptRoot/../e2e-ports" duplicate-file-a duplicate-file-b
+Throw-IfNotFailed
+if (-not $dupOutput.Contains('The following files are already installed')) {
+    throw ('Incorrect error message for due to duplicate files; output was ' + $dupOutput)
+}
+
 # Empty package / disable all checks
 Refresh-TestRoot
 [string]$buildOutput = Run-VcpkgAndCaptureStderr install @commonArgs --overlay-ports="$PSScriptRoot/../e2e-ports" vcpkg-policy-set-incorrectly
diff --git a/include/vcpkg/base/strings.h b/include/vcpkg/base/strings.h
index 8a0dc3d3ef..2d27d27b29 100644
--- a/include/vcpkg/base/strings.h
+++ b/include/vcpkg/base/strings.h
@@ -123,6 +123,7 @@ namespace vcpkg::Strings
     const char* case_insensitive_ascii_search(StringView s, StringView pattern);
     bool case_insensitive_ascii_contains(StringView s, StringView pattern);
     bool case_insensitive_ascii_equals(StringView left, StringView right);
+    bool case_insensitive_ascii_less(StringView left, StringView right);
 
     void inplace_ascii_to_lowercase(char* first, char* last);
     void inplace_ascii_to_lowercase(std::string& s);
diff --git a/src/vcpkg-test/strings.cpp b/src/vcpkg-test/strings.cpp
index 31db934147..de6a284db9 100644
--- a/src/vcpkg-test/strings.cpp
+++ b/src/vcpkg-test/strings.cpp
@@ -236,6 +236,26 @@ TEST_CASE ("api_stable_format(sv,append_f)", "[strings]")
     REQUIRE(*res.get() == "123hello456");
 }
 
+TEST_CASE ("lex compare less", "[strings]")
+{
+    REQUIRE(Strings::case_insensitive_ascii_less("a", "b"));
+    REQUIRE(Strings::case_insensitive_ascii_less("a", "B"));
+    REQUIRE(Strings::case_insensitive_ascii_less("A", "b"));
+    REQUIRE(Strings::case_insensitive_ascii_less("A", "B"));
+
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("b", "a"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("B", "a"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("b", "A"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("B", "A"));
+
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("b", "b"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("b", "B"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("B", "b"));
+
+    REQUIRE(Strings::case_insensitive_ascii_less("a", "aa"));
+    REQUIRE_FALSE(Strings::case_insensitive_ascii_less("aa", "a"));
+}
+
 #if defined(_WIN32)
 TEST_CASE ("ascii to utf16", "[utf16]")
 {
diff --git a/src/vcpkg/base/strings.cpp b/src/vcpkg/base/strings.cpp
index c308819c9e..34633102c7 100644
--- a/src/vcpkg/base/strings.cpp
+++ b/src/vcpkg/base/strings.cpp
@@ -104,6 +104,11 @@ namespace
         bool operator()(char a, char b) const noexcept { return tolower_char(a) == tolower_char(b); }
     } icase_eq;
 
+    constexpr struct
+    {
+        bool operator()(char a, char b) const noexcept { return tolower_char(a) < tolower_char(b); }
+    } icase_less;
+
 }
 
 #if defined(_WIN32)
@@ -173,6 +178,11 @@ bool Strings::case_insensitive_ascii_equals(StringView left, StringView right)
     return std::equal(left.begin(), left.end(), right.begin(), right.end(), icase_eq);
 }
 
+bool Strings::case_insensitive_ascii_less(StringView left, StringView right)
+{
+    return std::lexicographical_compare(left.begin(), left.end(), right.begin(), right.end(), icase_less);
+}
+
 void Strings::inplace_ascii_to_lowercase(char* first, char* last) { std::transform(first, last, first, tolower_char); }
 
 void Strings::inplace_ascii_to_lowercase(std::string& s)
diff --git a/src/vcpkg/commands.install.cpp b/src/vcpkg/commands.install.cpp
index 3c6270b030..2087e62835 100644
--- a/src/vcpkg/commands.install.cpp
+++ b/src/vcpkg/commands.install.cpp
@@ -231,14 +231,14 @@ namespace vcpkg
 
         struct intersection_compare
         {
-            // The VS2015 standard library requires comparison operators of T and U
-            // to also support comparison of T and T, and of U and U, due to debug checks.
-#if _MSC_VER <= 1910
-            bool operator()(const std::string& lhs, const std::string& rhs) const { return lhs < rhs; }
-            bool operator()(const file_pack& lhs, const file_pack& rhs) const { return lhs.first < rhs.first; }
-#endif
-            bool operator()(const std::string& lhs, const file_pack& rhs) const { return lhs < rhs.first; }
-            bool operator()(const file_pack& lhs, const std::string& rhs) const { return lhs.first < rhs; }
+            bool operator()(const std::string& lhs, const file_pack& rhs) const
+            {
+                return Strings::case_insensitive_ascii_less(lhs, rhs.first);
+            }
+            bool operator()(const file_pack& lhs, const std::string& rhs) const
+            {
+                return Strings::case_insensitive_ascii_less(lhs.first, rhs);
+            }
         };
 
         std::vector<file_pack> intersection;