diff --git a/changelog.d/15862.bugfix b/changelog.d/15862.bugfix
new file mode 100644
index 000000000..8eb6aa9a7
--- /dev/null
+++ b/changelog.d/15862.bugfix
@@ -0,0 +1,3 @@
+Pin `pydantic` to ^=1.7.4 to avoid backwards-incompatible API changes from the 2.0.0 release.
+Resolves https://github.com/matrix-org/synapse/issues/15858.
+Contributed by @PaarthShah.
diff --git a/poetry.lock b/poetry.lock
index 2802e42cf..9aaf5c7de 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1829,47 +1829,47 @@ files = [
 
 [[package]]
 name = "pydantic"
-version = "1.10.9"
+version = "1.10.10"
 description = "Data validation and settings management using python type hints"
 optional = false
 python-versions = ">=3.7"
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 ]
 
 [package.dependencies]
diff --git a/pyproject.toml b/pyproject.toml
index fc47b1ef7..67ee3f173 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -207,7 +207,8 @@ packaging = ">=16.1"
 # which shipped in Python 3.8. This corresponds to version 1.4 of the backport.
 importlib_metadata = { version = ">=1.4", python = "<3.8" }
 # This is the most recent version of Pydantic with available on common distros.
-pydantic = ">=1.7.4"
+# We are currently incompatible with >=2.0.0: (https://github.com/matrix-org/synapse/issues/15858)
+pydantic = "^1.7.4"
 
 # This is for building the rust components during "poetry install", which
 # currently ignores the `build-system.requires` directive (c.f.