diff --git a/flang/documentation/Intrinsics.md b/flang/documentation/Intrinsics.md
--- a/flang/documentation/Intrinsics.md
+++ b/flang/documentation/Intrinsics.md
@@ -701,7 +701,7 @@
 
 | Intrinsic Category | Intrinsic Procedures Lacking Support |
 | --- | --- |
-| Coarray intrinsic functions | LCOBOUND, UCOBOUND, FAILED_IMAGES, GET_TEAM, IMAGE_INDEX, NUM_IMAGES, STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE, COSHAPE |
+| Coarray intrinsic functions | LCOBOUND, UCOBOUND, FAILED_IMAGES, GET_TEAM, IMAGE_INDEX, STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE, COSHAPE |
 | Object characteristic inquiry functions | ALLOCATED, ASSOCIATED, EXTENDS_TYPE_OF, IS_CONTIGUOUS, PRESENT, RANK, SAME_TYPE, STORAGE_SIZE |
 | Type inquiry intrinsic functions | BIT_SIZE, DIGITS, EPSILON, HUGE, KIND, MAXEXPONENT, MINEXPONENT, NEW_LINE, PRECISION, RADIX, RANGE, TINY|
 | Non-standard intrinsic functions | AND, OR, XOR, LSHIFT, RSHIFT, SHIFT, ZEXT, IZEXT, COSD, SIND, TAND, ACOSD, ASIND, ATAND, ATAN2D, COMPL, DCMPLX, EQV, NEQV, INT8, JINT, JNINT, KNINT, LOC, QCMPLX, DREAL, DFLOAT, QEXT, QFLOAT, QREAL, DNUM, NUM, JNUM, KNUM, QNUM, RNUM, RAN, RANF, ILEN, SIZEOF, MCLOCK, SECNDS, COTAN, IBCHNG, ISHA, ISHC, ISHL, IXOR, IARG, IARGC, NARGS, NUMARG, BADDRESS, IADDR, CACHESIZE, EOF, FP_CLASS, INT_PTR_KIND, ISNAN, MALLOC |
diff --git a/flang/lib/Evaluate/intrinsics.cpp b/flang/lib/Evaluate/intrinsics.cpp
--- a/flang/lib/Evaluate/intrinsics.cpp
+++ b/flang/lib/Evaluate/intrinsics.cpp
@@ -581,6 +581,10 @@
         Rank::dimReduced, IntrinsicClass::transformationalFunction},
     {"not", {{"i", SameInt}}, SameInt},
     // NULL() is a special case handled in Probe() below
+    {"num_images", {}, DefaultInt, Rank::scalar,
+        IntrinsicClass::transformationalFunction},
+    {"num_images", {{"team_number", AnyInt, Rank::scalar}}, DefaultInt,
+        Rank::scalar, IntrinsicClass::transformationalFunction},
     {"out_of_range",
         {{"x", AnyIntOrReal}, {"mold", AnyIntOrReal, Rank::scalar}},
         DefaultLogical},
@@ -724,7 +728,7 @@
 
 // TODO: Coarray intrinsic functions
 //   LCOBOUND, UCOBOUND, FAILED_IMAGES, GET_TEAM, IMAGE_INDEX,
-//   NUM_IMAGES, STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE,
+//   STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE,
 //   COSHAPE
 // TODO: Non-standard intrinsic functions
 //  AND, OR, XOR, LSHIFT, RSHIFT, SHIFT, ZEXT, IZEXT,
diff --git a/flang/test/Semantics/call10.f90 b/flang/test/Semantics/call10.f90
--- a/flang/test/Semantics/call10.f90
+++ b/flang/test/Semantics/call10.f90
@@ -185,7 +185,6 @@
                                    ! implicit sync all
     !ERROR: Procedure 'this_image' referenced in pure subprogram 's14' must be pure too
     img = this_image()
-    !ERROR: Procedure 'num_images' referenced in pure subprogram 's14' must be pure too
     nimgs = num_images()
     i = img                       ! i is ready to use
 
diff --git a/flang/test/Semantics/num_images.f90 b/flang/test/Semantics/num_images.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/num_images.f90
@@ -0,0 +1,30 @@
+! RUN: %S/test_errors.sh %s %t %f18
+! Check for semantic errors in num_images() function calls
+
+subroutine test
+
+  ! correct calls, should produce no errors
+  print *, num_images()
+  print *, num_images(team_number=1)
+  print *, num_images(1)
+
+  ! incorrectly typed argument
+  ! the error is seen as too many arguments to the num_images() call with no arguments
+  !ERROR: too many actual arguments for intrinsic 'num_images'
+  print *, num_images(3.4)
+
+  ! call with too many arguments
+  !ERROR: too many actual arguments for intrinsic 'num_images'
+  print *, num_images(1, 1)
+
+  ! keyword argument with incorrect type
+  !ERROR: unknown keyword argument to intrinsic 'num_images'
+  print *, num_images(team_number=3.4)
+
+  ! incorrect keyword argument
+  !ERROR: unknown keyword argument to intrinsic 'num_images'
+  print *, num_images(team_numbers=1)
+
+  !TODO: test num_images() calls related to team_type argument
+
+end subroutine
diff --git a/flang/unittests/Evaluate/intrinsics.cpp b/flang/unittests/Evaluate/intrinsics.cpp
--- a/flang/unittests/Evaluate/intrinsics.cpp
+++ b/flang/unittests/Evaluate/intrinsics.cpp
@@ -257,6 +257,40 @@
   TestCall{defaults, table, "idint"}
       .Push(Const(Scalar<Real4>{}))
       .DoCall(Int4::GetType());
+
+  TestCall{defaults, table, "num_images"}.DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int1>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int4>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int8>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Named("team_number", Const(Scalar<Int4>{})))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int4>{}))
+      .Push(Const(Scalar<Int4>{}))
+      .DoCall(); // too many args
+  TestCall{defaults, table, "num_images"}
+      .Push(Named("bad", Const(Scalar<Int4>{})))
+      .DoCall(); // bad keyword
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Char>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Log4>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Complex8>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Real4>{}))
+      .DoCall(); // bad type
+
   // TODO: test other intrinsics
 }
 } // namespace Fortran::evaluate