Index: flang/lib/Lower/Allocatable.cpp
===================================================================
--- flang/lib/Lower/Allocatable.cpp
+++ flang/lib/Lower/Allocatable.cpp
@@ -558,8 +558,6 @@
     genAllocateObjectInit(box);
     if (alloc.hasCoarraySpec())
       TODO(loc, "coarray allocation");
-    if (alloc.getShapeSpecs().size() > 0 && sourceExv.rank() == 0)
-      TODO(loc, "allocate array object with scalar SOURCE specifier");
     // Set length of the allocate object if it has. Otherwise, get the length
     // from source for the deferred length parameter.
     if (lenParams.empty() && box.isCharacter() &&
Index: flang/runtime/allocatable.cpp
===================================================================
--- flang/runtime/allocatable.cpp
+++ flang/runtime/allocatable.cpp
@@ -126,8 +126,7 @@
       alloc, hasStat, errMsg, sourceFile, sourceLine)};
   if (stat == StatOk) {
     Terminator terminator{sourceFile, sourceLine};
-    // 9.7.1.2(7)
-    Assign(alloc, source, terminator, /*skipRealloc=*/true);
+    DoFromSourceAssign(alloc, source, terminator);
   }
   return stat;
 }
Index: flang/runtime/assign.h
===================================================================
--- flang/runtime/assign.h
+++ flang/runtime/assign.h
@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Internal APIs for data assignment (both intrinsic assignment and TBP defined
-// generic ASSIGNMENT(=)).
-
 #ifndef FORTRAN_RUNTIME_ASSIGN_INTERNAL_H_
 #define FORTRAN_RUNTIME_ASSIGN_INTERNAL_H_
 
@@ -16,15 +13,11 @@
 class Descriptor;
 class Terminator;
 
-// Assigns one object to another via intrinsic assignment (F'2018 10.2.1.3) or
-// type-bound (only!) defined assignment (10.2.1.4), as appropriate.  Performs
-// finalization, scalar expansion, & allocatable (re)allocation as needed.
-// Does not perform intrinsic assignment implicit type conversion.  Both
-// descriptors must be initialized.  Recurses as needed to handle components.
-// Do not perform allocatable reallocation if \p skipRealloc is true, which is
-// used for allocate statement with source specifier.
-void Assign(
-    Descriptor &, const Descriptor &, Terminator &, bool skipRealloc = false);
+// Assign one object to another via allocate statement from source specifier.
+// Note that if allocate object and source expression have the same rank, the
+// value of the allocate object becomes the value provided; otherwise the value
+// of each element of allocate object becomes the value provided (9.7.1.2(7)).
+void DoFromSourceAssign(Descriptor &, const Descriptor &, Terminator &);
 
 } // namespace Fortran::runtime
 #endif // FORTRAN_RUNTIME_ASSIGN_INTERNAL_H_
Index: flang/runtime/assign.cpp
===================================================================
--- flang/runtime/assign.cpp
+++ flang/runtime/assign.cpp
@@ -60,8 +60,15 @@
   }
 }
 
-void Assign(Descriptor &to, const Descriptor &from, Terminator &terminator,
-    bool skipRealloc) {
+// Assigns one object to another via intrinsic assignment (F'2018 10.2.1.3) or
+// type-bound (only!) defined assignment (10.2.1.4), as appropriate.  Performs
+// finalization, scalar expansion, & allocatable (re)allocation as needed.
+// Does not perform intrinsic assignment implicit type conversion.  Both
+// descriptors must be initialized.  Recurses as needed to handle components.
+// Do not perform allocatable reallocation if \p skipRealloc is true, which is
+// used for allocate statement with source specifier.
+static void Assign(Descriptor &to, const Descriptor &from,
+    Terminator &terminator, bool skipRealloc = false) {
   DescriptorAddendum *toAddendum{to.Addendum()};
   const typeInfo::DerivedType *toDerived{
       toAddendum ? toAddendum->derivedType() : nullptr};
@@ -276,6 +283,33 @@
   }
 }
 
+void DoFromSourceAssign(
+    Descriptor &alloc, const Descriptor &source, Terminator &terminator) {
+  if (alloc.rank() > 0 && source.rank() == 0) {
+    // The value of each element of allocate object becomes the value of source.
+    DescriptorAddendum *allocAddendum{alloc.Addendum()};
+    SubscriptValue allocAt[maxRank];
+    alloc.GetLowerBounds(allocAt);
+    if (allocAddendum) {
+      const typeInfo::DerivedType *allocDerived{allocAddendum->derivedType()};
+      for (std::size_t n{alloc.Elements()}; n-- > 0;
+           alloc.IncrementSubscripts(allocAt)) {
+        Descriptor allocElement{*Descriptor::Create(*allocDerived,
+            reinterpret_cast<void *>(alloc.Element<char>(allocAt)), 0)};
+        Assign(allocElement, source, terminator, /*skipRealloc=*/true);
+      }
+    } else { // intrinsic type
+      for (std::size_t n{alloc.Elements()}; n-- > 0;
+           alloc.IncrementSubscripts(allocAt)) {
+        std::memmove(alloc.Element<char>(allocAt), source.raw().base_addr,
+            alloc.ElementBytes());
+      }
+    }
+  } else {
+    Assign(alloc, source, terminator, /*skipRealloc=*/true);
+  }
+}
+
 extern "C" {
 void RTNAME(Assign)(Descriptor &to, const Descriptor &from,
     const char *sourceFile, int sourceLine) {
Index: flang/runtime/pointer.cpp
===================================================================
--- flang/runtime/pointer.cpp
+++ flang/runtime/pointer.cpp
@@ -143,8 +143,7 @@
       pointer, hasStat, errMsg, sourceFile, sourceLine)};
   if (stat == StatOk) {
     Terminator terminator{sourceFile, sourceLine};
-    // 9.7.1.2(7)
-    Assign(pointer, source, terminator, /*skipRealloc=*/true);
+    DoFromSourceAssign(pointer, source, terminator);
   }
   return stat;
 }