diff --git a/.changelog/118.txt b/.changelog/118.txt
new file mode 100644
index 000000000..b2c70c61d
--- /dev/null
+++ b/.changelog/118.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+tfsdk: Don't attempt validation on the nested attributes of a null or unknown `SingleNestedAttribute`
+```
\ No newline at end of file
diff --git a/tfsdk/attribute.go b/tfsdk/attribute.go
index d1d39c4f4..55c1770c4 100644
--- a/tfsdk/attribute.go
+++ b/tfsdk/attribute.go
@@ -341,18 +341,33 @@ func (a Attribute) validate(ctx context.Context, req ValidateAttributeRequest, r
 				}
 			}
 		case NestingModeSingle:
-			for nestedName, nestedAttr := range a.Attributes.GetAttributes() {
-				nestedAttrReq := ValidateAttributeRequest{
-					AttributePath: req.AttributePath.WithAttributeName(nestedName),
-					Config:        req.Config,
-				}
-				nestedAttrResp := &ValidateAttributeResponse{
-					Diagnostics: resp.Diagnostics,
-				}
+			o, ok := req.AttributeConfig.(types.Object)
+
+			if !ok {
+				err := fmt.Errorf("unknown attribute value type (%T) for nesting mode (%T) at path: %s", req.AttributeConfig, nm, req.AttributePath)
+				resp.Diagnostics.AddAttributeError(
+					req.AttributePath,
+					"Attribute Validation Error",
+					"Attribute validation cannot walk schema. Report this to the provider developer:\n\n"+err.Error(),
+				)
+
+				return
+			}
+
+			if !o.Null && !o.Unknown {
+				for nestedName, nestedAttr := range a.Attributes.GetAttributes() {
+					nestedAttrReq := ValidateAttributeRequest{
+						AttributePath: req.AttributePath.WithAttributeName(nestedName),
+						Config:        req.Config,
+					}
+					nestedAttrResp := &ValidateAttributeResponse{
+						Diagnostics: resp.Diagnostics,
+					}
 
-				nestedAttr.validate(ctx, nestedAttrReq, nestedAttrResp)
+					nestedAttr.validate(ctx, nestedAttrReq, nestedAttrResp)
 
-				resp.Diagnostics = nestedAttrResp.Diagnostics
+					resp.Diagnostics = nestedAttrResp.Diagnostics
+				}
 			}
 		default:
 			err := fmt.Errorf("unknown attribute validation nesting mode (%T: %v) at path: %s", nm, nm, req.AttributePath)