diff --git a/docs/configuration.rst b/docs/configuration.rst
index 8620c6da..6e26b3dd 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -911,7 +911,8 @@ The configurable runtime parameters of each source are as follows:
 
 * ``'PRESCRIBED'``
     Source values are arbitrarily prescribed by the user. The value is set by ``prescribed_values``, and can contain the same
-    data structures as :ref:`Time-varying arrays`.
+    data structures as :ref:`Time-varying arrays`. Currently, this is only supported for sources that have a 1D output
+    along the cell grid or face grid.
 
 For example, to set 'fusion_power' to zero, e.g. for testing or sensitivity purposes, set:
 
diff --git a/torax/sources/runtime_params.py b/torax/sources/runtime_params.py
index 1cd244ea..d5222ea7 100644
--- a/torax/sources/runtime_params.py
+++ b/torax/sources/runtime_params.py
@@ -34,7 +34,7 @@
 class Mode(enum.Enum):
   """Defines how to compute the source terms for this source/sink."""
 
-  # Source is set to zero always. This is an explicit source by definition.
+  # Source is set to zero always.
   ZERO = 0
 
   # Source values come from a model in code. These terms can be implicit or
@@ -42,8 +42,8 @@ class Mode(enum.Enum):
   MODEL_BASED = 1
 
   # Source values come from a pre-determined set of values, that may evolve in
-  # time. Values can be drawn from a file or an array. These sources are always
-  # explicit.
+  # time. Currently, this is only supported for sources that have a 1D output
+  # along the cell grid or face grid.
   PRESCRIBED = 2