diff --git a/conda_build/variants.py b/conda_build/variants.py
index ed21daf806..f0531b8353 100644
--- a/conda_build/variants.py
+++ b/conda_build/variants.py
@@ -329,7 +329,7 @@ def _combine_spec_dictionaries(
                                     ) != len(ensure_list(v)):
                                         break
                                 else:
-                                    values[k] = v.copy()
+                                    values[k] = copy(v)
                                 missing_subvalues = [
                                     subvalue
                                     for subvalue in ensure_list(v)
diff --git a/news/5417-fix-str-copy.rst b/news/5417-fix-str-copy.rst
new file mode 100644
index 0000000000..ddac53eedc
--- /dev/null
+++ b/news/5417-fix-str-copy.rst
@@ -0,0 +1,19 @@
+### Enhancements
+
+* <news item>
+
+### Bug fixes
+
+* Fixed a bug where ``.copy()`` was used on a string instead of ``copy()`` when processing variants. (#5417)
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>
diff --git a/tests/test_variants.py b/tests/test_variants.py
index 572d6362bf..95ac31bcb1 100644
--- a/tests/test_variants.py
+++ b/tests/test_variants.py
@@ -899,3 +899,164 @@ def test_find_used_variables_in_batch_script(tmp_path: Path) -> None:
         f"${{{variants[3]}}}\n"
     )
     assert find_used_variables_in_batch_script(variants, script) == {"FOO", "BAR"}
+
+
+def test_combine_specs_zip_lengths():
+    from collections import OrderedDict
+
+    # test case extracted from issue #5416
+    specs = OrderedDict(
+        [
+            (
+                "internal_defaults",
+                {
+                    "c_compiler": "gcc",
+                    "cpu_optimization_target": "nocona",
+                    "cran_mirror": "https://cran.r-project.org",
+                    "cxx_compiler": "gxx",
+                    "extend_keys": [
+                        "pin_run_as_build",
+                        "ignore_version",
+                        "ignore_build_only_deps",
+                        "extend_keys",
+                    ],
+                    "fortran_compiler": "gfortran",
+                    "ignore_build_only_deps": ["python", "numpy"],
+                    "ignore_version": [],
+                    "lua": "5",
+                    "numpy": "1.23",
+                    "perl": "5.26.2",
+                    "pin_run_as_build": {
+                        "python": {"max_pin": "x.x", "min_pin": "x.x"},
+                        "r-base": {"max_pin": "x.x", "min_pin": "x.x"},
+                    },
+                    "python": "3.11",
+                    "r_base": "3.5",
+                    "target_platform": "linux-64",
+                },
+            ),
+            (
+                "/tmp/tmp0wue6mdn/info/recipe/conda_build_config.yaml",
+                {
+                    "VERBOSE_AT": "V=1",
+                    "VERBOSE_CM": "VERBOSE=1",
+                    "blas_impl": "openblas",
+                    "boost": "1.82",
+                    "boost_cpp": "1.82",
+                    "bzip2": "1.0",
+                    "c_compiler": "gcc",
+                    "c_compiler_version": "11.2.0",
+                    "cairo": "1.16",
+                    "channel_targets": "defaults",
+                    "clang_variant": "clang",
+                    "cpu_optimization_target": "nocona",
+                    "cran_mirror": "https://mran.microsoft.com/snapshot/2018-01-01",
+                    "cuda_compiler": "cuda-nvcc",
+                    "cuda_compiler_version": "12.4",
+                    "cudatoolkit": "11.8",
+                    "cudnn": "8.9.2.26",
+                    "cxx_compiler": "gxx",
+                    "cxx_compiler_version": "11.2.0",
+                    "cyrus_sasl": "2.1.28",
+                    "dbus": "1",
+                    "expat": "2",
+                    "extend_keys": [
+                        "pin_run_as_build",
+                        "extend_keys",
+                        "ignore_build_only_deps",
+                        "ignore_version",
+                    ],
+                    "fontconfig": "2.14",
+                    "fortran_compiler": "gfortran",
+                    "fortran_compiler_version": "11.2.0",
+                    "freetype": "2.10",
+                    "g2clib": "1.6",
+                    "geos": "3.8.0",
+                    "giflib": "5",
+                    "glib": "2",
+                    "gmp": "6.2",
+                    "gnu": "2.12.2",
+                    "gpu_variant": "cuda-11",
+                    "gst_plugins_base": "1.14",
+                    "gstreamer": "1.14",
+                    "harfbuzz": "4.3.0",
+                    "hdf4": "4.2",
+                    "hdf5": "1.12.1",
+                    "hdfeos2": "2.20",
+                    "hdfeos5": "5.1",
+                    "icu": "73",
+                    "ignore_build_only_deps": ["python", "numpy"],
+                    "jpeg": "9",
+                    "libcurl": "8.1.1",
+                    "libdap4": "3.19",
+                    "libffi": "3.4",
+                    "libgd": "2.3.3",
+                    "libgdal": "3.6.2",
+                    "libgsasl": "1.10",
+                    "libkml": "1.3",
+                    "libnetcdf": "4.8",
+                    "libpng": "1.6",
+                    "libprotobuf": "3.20.3",
+                    "libtiff": "4.2",
+                    "libwebp": "1.3.2",
+                    "libxml2": "2.10",
+                    "libxslt": "1.1",
+                    "llvm_variant": "llvm",
+                    "lua": "5",
+                    "lzo": "2",
+                    "mkl": "2023.*",
+                    "mpfr": "4",
+                    "numpy": "1.21",
+                    "openblas": "0.3.21",
+                    "openjpeg": "2.3",
+                    "openssl": "3.0",
+                    "perl": "5.34",
+                    "pin_run_as_build": {
+                        "libboost": {"max_pin": "x.x.x"},
+                        "python": {"max_pin": "x.x", "min_pin": "x.x"},
+                        "r-base": {"max_pin": "x.x", "min_pin": "x.x"},
+                    },
+                    "pixman": "0.40",
+                    "proj": "9.3.1",
+                    "proj4": "5.2.0",
+                    "python": "3.9",
+                    "python_impl": "cpython",
+                    "python_implementation": "cpython",
+                    "r_base": "3.5",
+                    "r_implementation": "r-base",
+                    "r_version": "3.5.0",
+                    "readline": "8.1",
+                    "rust_compiler": "rust",
+                    "rust_compiler_version": "1.71.1",
+                    "sqlite": "3",
+                    "target_platform": "linux-64",
+                    "tk": "8.6",
+                    "xz": "5",
+                    "zip_keys": [["python", "numpy"]],
+                    "zlib": "1.2",
+                    "zstd": "1.5.2",
+                },
+            ),
+            (
+                "config.variant",
+                {
+                    "__cuda": "__cuda >=11.8",
+                    "blas_impl": "openblas",
+                    "c_compiler": "gcc",
+                    "c_compiler_version": "11.2.0",
+                    "channel_targets": "defaults",
+                    "cudatoolkit": "11.8",
+                    "cudnn": "8.9.2.26",
+                    "cxx_compiler": "gxx",
+                    "cxx_compiler_version": "11.2.0",
+                    "gpu_variant": "cuda-11",
+                    "libprotobuf": "3.20.3",
+                    "numpy": "1.21",
+                    "openblas": "0.3.21",
+                    "target_platform": "linux-64",
+                },
+            ),
+        ]
+    )
+
+    combine_specs(specs, log_output=True)