diff --git a/README.md b/README.md
index 0bac36c..2ff0849 100644
--- a/README.md
+++ b/README.md
@@ -204,6 +204,7 @@ When contributing to this library, it is therefore important to ensure that all
 
 We are currently on major release v4.  Breaking changes should be marked with the [deprecated](https://www.doxygen.nl/manual/commands.html#cmddeprecated) doxygen tag.  The following changes are planned when the next major/breaking release (v5) becomes necessary:
 
+* mf_getuniquelibref.sas to have the deprecated maxtried parameter removed (no longer needed)
 * mp_testservice.sas to be renamed as mp_execute.sas (as it doesn't actually test anything)
 * `insert_cmplib` option of mcf_xxx macros will be deprecated (the option is now checked automatically with value inserted only if needed)
 * mcf_xxx macros to have `wrap=` option defaulted to YES for convenience.  Set this option explicitly to avoid issues.
diff --git a/all.sas b/all.sas
index f0f0b21..6f17814 100644
--- a/all.sas
+++ b/all.sas
@@ -970,29 +970,46 @@ or %index(&pgm,/tests/testteardown)
 
 > mclib3
 
-  @param prefix= first part of libref.  Remember that librefs can only be 8 characters,
-    so a 7 letter prefix would mean that maxtries should be 10.
-  @param maxtries= the last part of the libref.  Provide an integer value.
+  A blank value is returned if no usable libname is determined.
+
+  @param [in] prefix= (mclib) first part of the returned libref. As librefs can
+    be as long as 8 characters, a maximum length of 7 characters is premitted
+    for this prefix.
+  @param [in] maxtries= Deprecated parameter. Remains here to ensure a
+    non-breaking change.  Will be removed in v5.
 
   @version 9.2
   @author Allan Bowe
 **/
 
-
 %macro mf_getuniquelibref(prefix=mclib,maxtries=1000);
-  %local x libref;
-  %let x=0;
-  %do x=0 %to &maxtries;
-  %if %sysfunc(libref(&prefix&x)) ne 0 %then %do;
-    %let libref=&prefix&x;
-    %let rc=%sysfunc(libname(&libref,%sysfunc(pathname(work))));
-    %if &rc %then %put %sysfunc(sysmsg());
-    &prefix&x
-    %*put &sysmacroname: Libref &libref assigned as WORK and returned;
+  %local x;
+
+  %if ( %length(&prefix) gt 7 ) %then %do;
+    %put %str(ERR)OR: The prefix parameter cannot exceed 7 characters.;
+    0
     %return;
   %end;
+  %else %if (%sysfunc(NVALID(&prefix,v7))=0) %then %do;
+    %put %str(ERR)OR: Invalid prefix (&prefix);
+    0
+    %return;
   %end;
-  %put unable to find available libref in range &prefix.0-&maxtries;
+
+  /* Set maxtries equal to '10 to the power of [# unused characters] - 1' */
+  %let maxtries=%eval(10**(8-%length(&prefix))-1);
+
+  %do x = 0 %to &maxtries;
+    %if %sysfunc(libref(&prefix&x)) ne 0 %then %do;
+      &prefix&x
+      %return;
+    %end;
+    %let x = %eval(&x + 1);
+  %end;
+
+  %put %str(ERR)OR: No usable libref in range &prefix.0-&maxtries;
+  %put %str(ERR)OR- Try reducing the prefix or deleting some libraries!;
+  0
 %mend mf_getuniquelibref;/**
   @file mf_getuniquename.sas
   @brief Returns a shortened (32 char) GUID as a valid SAS name
@@ -3146,7 +3163,9 @@ run;
 
   %let ds=&syslast;
 
-  proc compare base=&scopeds compare=&ds;
+  proc compare
+    base=&scopeds(where=(upcase(name) not in (%mf_getquotedstr(&ilist))))
+    compare=&ds;
   run;
 
   %if &sysinfo=0 %then %do;
diff --git a/base/mf_getuniquelibref.sas b/base/mf_getuniquelibref.sas
index 8fe1ef9..c5eb387 100644
--- a/base/mf_getuniquelibref.sas
+++ b/base/mf_getuniquelibref.sas
@@ -14,27 +14,44 @@
 
 > mclib3
 
-  @param prefix= first part of libref.  Remember that librefs can only be 8 characters,
-    so a 7 letter prefix would mean that maxtries should be 10.
-  @param maxtries= the last part of the libref.  Provide an integer value.
+  A blank value is returned if no usable libname is determined.
+
+  @param [in] prefix= (mclib) first part of the returned libref. As librefs can
+    be as long as 8 characters, a maximum length of 7 characters is premitted
+    for this prefix.
+  @param [in] maxtries= Deprecated parameter. Remains here to ensure a
+    non-breaking change.  Will be removed in v5.
 
   @version 9.2
   @author Allan Bowe
 **/
 
-
 %macro mf_getuniquelibref(prefix=mclib,maxtries=1000);
-  %local x libref;
-  %let x=0;
-  %do x=0 %to &maxtries;
-  %if %sysfunc(libref(&prefix&x)) ne 0 %then %do;
-    %let libref=&prefix&x;
-    %let rc=%sysfunc(libname(&libref,%sysfunc(pathname(work))));
-    %if &rc %then %put %sysfunc(sysmsg());
-    &prefix&x
-    %*put &sysmacroname: Libref &libref assigned as WORK and returned;
+  %local x;
+
+  %if ( %length(&prefix) gt 7 ) %then %do;
+    %put %str(ERR)OR: The prefix parameter cannot exceed 7 characters.;
+    0
     %return;
   %end;
+  %else %if (%sysfunc(NVALID(&prefix,v7))=0) %then %do;
+    %put %str(ERR)OR: Invalid prefix (&prefix);
+    0
+    %return;
   %end;
-  %put unable to find available libref in range &prefix.0-&maxtries;
+
+  /* Set maxtries equal to '10 to the power of [# unused characters] - 1' */
+  %let maxtries=%eval(10**(8-%length(&prefix))-1);
+
+  %do x = 0 %to &maxtries;
+    %if %sysfunc(libref(&prefix&x)) ne 0 %then %do;
+      &prefix&x
+      %return;
+    %end;
+    %let x = %eval(&x + 1);
+  %end;
+
+  %put %str(ERR)OR: No usable libref in range &prefix.0-&maxtries;
+  %put %str(ERR)OR- Try reducing the prefix or deleting some libraries!;
+  0
 %mend mf_getuniquelibref;
\ No newline at end of file
diff --git a/base/mp_assertscope.sas b/base/mp_assertscope.sas
index 786361c..5421371 100644
--- a/base/mp_assertscope.sas
+++ b/base/mp_assertscope.sas
@@ -104,7 +104,9 @@
 
   %let ds=&syslast;
 
-  proc compare base=&scopeds compare=&ds;
+  proc compare
+    base=&scopeds(where=(upcase(name) not in (%mf_getquotedstr(&ilist))))
+    compare=&ds;
   run;
 
   %if &sysinfo=0 %then %do;
diff --git a/tests/crossplatform/mf_getuniquelibref.test.sas b/tests/crossplatform/mf_getuniquelibref.test.sas
new file mode 100644
index 0000000..16ecc4b
--- /dev/null
+++ b/tests/crossplatform/mf_getuniquelibref.test.sas
@@ -0,0 +1,54 @@
+/**
+  @file
+  @brief Testing mf_getuniquelibref macro
+  @details To test performance you can also use the following macro:
+
+  <h4> SAS Macros </h4>
+  @li mf_getuniquelibref.sas
+  @li mp_assert.sas
+  @li mp_assertscope.sas
+
+**/
+
+/* check valid libs */
+%mp_assertscope(SNAPSHOT)
+%let libshort=%mf_getuniquelibref(prefix=lib);
+%mp_assertscope(COMPARE,ignorelist=LIBSHORT)
+libname &libshort (work);
+%mp_assert(
+  iftrue=(&syscc=0),
+  desc=Checking for valid libref &libshort,
+  outds=work.test_results
+)
+
+%let lib7=%mf_getuniquelibref(prefix=libref7);
+libname &lib7 (work);
+%mp_assert(
+  iftrue=(&syscc=0),
+  desc=Checking for valid libref &lib7,
+  outds=work.test_results
+)
+
+
+/* check for invalid libs */
+
+%let lib8=%mf_getuniquelibref(prefix=lib8char);
+%mp_assert(
+  iftrue=(&lib8=0),
+  desc=Invalid prefix (8 chars),
+  outds=work.test_results
+)
+
+%let liblong=%mf_getuniquelibref(prefix=invalidlib);
+%mp_assert(
+  iftrue=(&liblong=0),
+  desc=Checking for invalid libref (long),
+  outds=work.test_results
+)
+
+%let badlib=%mf_getuniquelibref(prefix=8adlib);
+%mp_assert(
+  iftrue=(&badlib=0),
+  desc=Checking for invalid libref (8adlib),
+  outds=work.test_results
+)
\ No newline at end of file