diff --git a/include/API/errors.h b/include/API/errors.h
index 4e7859c21..e5ac61f77 100644
--- a/include/API/errors.h
+++ b/include/API/errors.h
@@ -32,6 +32,7 @@ namespace qssc {
 
 enum class ErrorCategory {
   OpenQASM3ParseFailure,
+  OpenQASM3UnsupportedInput,
   QSSCompilerError,
   QSSCompilerNoInputError,
   QSSCompilerCommunicationFailure,
diff --git a/python_lib/qss_compiler/exceptions.py b/python_lib/qss_compiler/exceptions.py
index 41b057500..bff21fa99 100644
--- a/python_lib/qss_compiler/exceptions.py
+++ b/python_lib/qss_compiler/exceptions.py
@@ -119,3 +119,7 @@ class QSSControlSystemResourcesExceeded(QSSCompilerError):
 
 class OpenQASM3ParseFailure(QSSCompilerError):
     """Raised when a parser failure is received"""
+
+
+class OpenQASM3UnsupportedInput(QSSCompilerError):
+    """Raised when provided Openqasm 3 input has semantics that are not supported by the compiler."""
diff --git a/python_lib/qss_compiler/lib_enums.cpp b/python_lib/qss_compiler/lib_enums.cpp
index 3789afff5..e2ec63ded 100644
--- a/python_lib/qss_compiler/lib_enums.cpp
+++ b/python_lib/qss_compiler/lib_enums.cpp
@@ -15,6 +15,7 @@ void addErrorCategory(py::module &m) {
   py::enum_<qssc::ErrorCategory>(m, "ErrorCategory", py::arithmetic())
       .value("OpenQASM3ParseFailure",
              qssc::ErrorCategory::OpenQASM3ParseFailure)
+      .value("OpenQASM3UnsupportedInput", qssc::ErrorCategory::OpenQASM3UnsupportedInput)
       .value("QSSCompilerError", qssc::ErrorCategory::QSSCompilerError)
       .value("QSSCompilerNoInputError",
              qssc::ErrorCategory::QSSCompilerNoInputError)
diff --git a/releasenotes/notes/add-unsupported-openqasm3-input-a584bb990cd9c9ff.yaml b/releasenotes/notes/add-unsupported-openqasm3-input-a584bb990cd9c9ff.yaml
new file mode 100644
index 000000000..23a48b3c1
--- /dev/null
+++ b/releasenotes/notes/add-unsupported-openqasm3-input-a584bb990cd9c9ff.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    A new diagnostic has been added for unsupported OpenQASM 3 semantics - ``OpenQASM3UnsupportedInput``.
+    This should be raised when the input OpenQASM 3 semantics are not valid for the compiler.
+