diff --git a/flang/lib/Semantics/resolve-names-utils.cpp b/flang/lib/Semantics/resolve-names-utils.cpp
index a838d49c06104..347f54e064070 100644
--- a/flang/lib/Semantics/resolve-names-utils.cpp
+++ b/flang/lib/Semantics/resolve-names-utils.cpp
@@ -762,7 +762,11 @@ void SymbolMapper::MapSymbolExprs(Symbol &symbol) {
               proc.set_procInterfaces(
                   *mappedSymbol, BypassGeneric(mappedSymbol->GetUltimate()));
             } else if (const DeclTypeSpec * mappedType{MapType(proc.type())}) {
-              proc.set_type(*mappedType);
+              if (proc.type()) {
+                CHECK(*proc.type() == *mappedType);
+              } else {
+                proc.set_type(*mappedType);
+              }
             }
             if (proc.init()) {
               if (const Symbol * mapped{MapSymbol(*proc.init())}) {
diff --git a/flang/test/Semantics/bug124487.f90 b/flang/test/Semantics/bug124487.f90
new file mode 100644
index 0000000000000..b91757c362367
--- /dev/null
+++ b/flang/test/Semantics/bug124487.f90
@@ -0,0 +1,14 @@
+!RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck --allow-empty %s
+!CHECK-NOT: error:
+module m
+  interface
+    module subroutine smp(x)
+      character, external :: x
+    end
+  end interface
+end
+submodule (m) sm
+ contains
+  module procedure smp ! crashes here
+  end
+end