diff --git a/states/statefile/version3_upgrade.go b/states/statefile/version3_upgrade.go
index 64c3c1afb..753298ff0 100644
--- a/states/statefile/version3_upgrade.go
+++ b/states/statefile/version3_upgrade.go
@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/zclconf/go-cty/cty"
 	ctyjson "github.com/zclconf/go-cty/cty/json"
 
@@ -51,6 +52,13 @@ func upgradeStateV3ToV4(old *stateV3) (*stateV4, error) {
 		// all of the modules are unkeyed.
 		moduleAddr := make(addrs.ModuleInstance, len(msOld.Path)-1)
 		for i, name := range msOld.Path[1:] {
+			if !hclsyntax.ValidIdentifier(name) {
+				// If we don't fail here then we'll produce an invalid state
+				// version 4 which subsequent operations will reject, so we'll
+				// fail early here for safety to make sure we can never
+				// inadvertently commit an invalid snapshot to a backend.
+				return nil, fmt.Errorf("state contains invalid module path %#v: %q is not a valid identifier; rename it in Terraform 0.11 before upgrading to Terraform 0.12", msOld.Path, name)
+			}
 			moduleAddr[i] = addrs.ModuleInstanceStep{
 				Name:        name,
 				InstanceKey: addrs.NoKey,
@@ -99,6 +107,13 @@ func upgradeStateV3ToV4(old *stateV3) (*stateV4, error) {
 					var diags tfdiags.Diagnostics
 					providerAddr, diags = addrs.ParseAbsProviderConfigStr(oldProviderAddr)
 					if diags.HasErrors() {
+						if strings.Contains(oldProviderAddr, "${") {
+							// There seems to be a common misconception that
+							// interpolation was valid in provider aliases
+							// in 0.11, so we'll use a specialized error
+							// message for that case.
+							return nil, fmt.Errorf("invalid provider config reference %q for %s: this alias seems to contain a template interpolation sequence, which was not supported but also not error-checked in Terraform 0.11. To proceed, rename the associated provider alias to a valid identifier and apply the change with Terraform 0.11 before upgrading to Terraform 0.12", oldProviderAddr, instAddr)
+						}
 						return nil, fmt.Errorf("invalid provider config reference %q for %s: %s", oldProviderAddr, instAddr, diags.Err())
 					}
 				} else {
@@ -110,6 +125,13 @@ func upgradeStateV3ToV4(old *stateV3) (*stateV4, error) {
 					if oldProviderAddr != "" {
 						localAddr, diags := addrs.ParseProviderConfigCompactStr(oldProviderAddr)
 						if diags.HasErrors() {
+							if strings.Contains(oldProviderAddr, "${") {
+								// There seems to be a common misconception that
+								// interpolation was valid in provider aliases
+								// in 0.11, so we'll use a specialized error
+								// message for that case.
+								return nil, fmt.Errorf("invalid legacy provider config reference %q for %s: this alias seems to contain a template interpolation sequence, which was not supported but also not error-checked in Terraform 0.11. To proceed, rename the associated provider alias to a valid identifier and apply the change with Terraform 0.11 before upgrading to Terraform 0.12", oldProviderAddr, instAddr)
+							}
 							return nil, fmt.Errorf("invalid legacy provider config reference %q for %s: %s", oldProviderAddr, instAddr, diags.Err())
 						}
 						providerAddr = localAddr.Absolute(moduleAddr)
diff --git a/website/upgrade-guides/0-12.html.markdown b/website/upgrade-guides/0-12.html.markdown
index d5a3c432b..b4e9ca741 100644
--- a/website/upgrade-guides/0-12.html.markdown
+++ b/website/upgrade-guides/0-12.html.markdown
@@ -106,6 +106,31 @@ After all of the tasks are complete, run `terraform 0.12checklist` one more time
 to verify that everything is complete. If so, continue reading the following
 sections to complete the upgrade!
 
+### Addendum: Invalid module names
+
+There is one additional pre-upgrade checklist item that the Terraform team did
+not become aware of until after the release of Terraform v0.11.14, and thus
+cannot be detected automatically by the checklist tool: renaming modules which
+have names that start with digits.
+
+Terraform 0.11 inadvertently tolerated leading-digit names for modules as a
+result of a validation bug, but Terraform 0.12 has corrected that bug and will
+reject such module names. Unfortunately, module names are also recorded in
+state snapshots and so a state snapshot created for a configuration with an
+invalid module name will itself be invalid as far as Terraform 0.12 is
+concerned.
+
+You can address this in a similar way to what the checklist tool suggests for
+invalid resource names and provider aliases:
+
+* Rename the module in your configuration.
+* Use `terraform state mv module.old module.new` _in Terraform 0.11.14_ to
+  update the state to use the new name instead of the old name.
+
+As with all of the pre-upgrade checklist items, be sure to run `terraform apply`
+once more before upgrading in order to ensure that the latest state snapshot is
+synchronized with the latest configuration.
+
 ## Upgrading to Terraform 0.12
 
 Before switching to Terraform 0.12, we recommend using Terraform v0.11.14 (or