diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b592d98..393e17c8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,13 @@
+Unreleased
+  - Added `blas_symbol_suffix` option (and `BLAS_FORTRAN_SUFFIX` compile
+    define) for linking against BLAS libraries whose Fortran symbols carry
+    a suffix, e.g. OpenBLAS built with `INTERFACE64=1 SYMBOLSUFFIX=64_`
+    exports `dgemm_64_`. Empty (default) preserves existing behavior. When
+    set, the OpenBLAS search probe links `-lopenblas${blas_symbol_suffix}`.
+    Supported by both the CMake and Make (`configure.py`) builds.
+  - The OpenBLAS search now also probes `-lopenblas64`, so the ILP64 build
+    Debian/Ubuntu ship as `libopenblas64` is found automatically.
+
 2025.05.28 (ABI 2.0.0)
   - Added Level 1 BLAS GPU wrappers
   - Added is_complex_v
diff --git a/CMakeLists.txt b/CMakeLists.txt
index cbb96243..88e63972 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -122,6 +122,9 @@ set_property(
     CACHE blas_int PROPERTY STRINGS
     "auto" "int (LP64)" "int64_t (ILP64)" )
 
+set( blas_symbol_suffix "" CACHE STRING
+     "Suffix appended to BLAS symbol names after Fortran mangling, e.g. '64_' for OpenBLAS built with INTERFACE64=1 SYMBOLSUFFIX=64_. Empty (default) preserves existing behavior." )
+
 set( blas_threaded "auto" CACHE STRING
      "Multi-threaded BLAS?" )
 set_property(
@@ -146,6 +149,7 @@ BLA_VENDOR             = ${BLA_VENDOR}
 blas                   = ${blas}
 blas_fortran           = ${blas_fortran}
 blas_int               = ${blas_int}
+blas_symbol_suffix     = ${blas_symbol_suffix}
 blas_threaded          = ${blas_threaded}
 lapack                 = ${lapack}
 build_tests            = ${build_tests}
diff --git a/cmake/BLASFinder.cmake b/cmake/BLASFinder.cmake
index 2994f855..1237d104 100644
--- a/cmake/BLASFinder.cmake
+++ b/cmake/BLASFinder.cmake
@@ -382,6 +382,17 @@ if (test_openblas)
     # todo: OPENBLAS_?(ROOT|DIR)
     list( APPEND blas_name_list "OpenBLAS" )
     list( APPEND blas_libs_list "-lopenblas" )
+    # Debian/Ubuntu ship the ILP64 build as libopenblas64, with standard
+    # (unsuffixed) dgemm_ symbols, so it needs only the -lopenblas64 name.
+    list( APPEND blas_name_list "OpenBLAS (ILP64, -lopenblas64)" )
+    list( APPEND blas_libs_list "-lopenblas64" )
+    # OpenBLAS built with SYMBOLSUFFIX (e.g. conda-forge's libopenblas64_,
+    # exporting dgemm_64_) follows the same naming; blas_symbol_suffix adds
+    # both the suffixed link name and the BLAS_FORTRAN_SUFFIX define (below).
+    if (blas_symbol_suffix)
+        list( APPEND blas_name_list "OpenBLAS (symbol suffix '${blas_symbol_suffix}')" )
+        list( APPEND blas_libs_list "-lopenblas${blas_symbol_suffix}" )
+    endif()
     debug_print_list( "openblas" )
 endif()
 
@@ -420,6 +431,14 @@ endif()
 set( BLAS_FOUND false )
 unset( blaspp_defs_ CACHE )
 
+# Extra define to forward to the link/run probes when the user has
+# requested a BLAS symbol suffix. Kept separate from the mangling
+# loop because it is orthogonal to UPPER/LOWER/ADD_.
+set( blas_symbol_suffix_def "" )
+if (blas_symbol_suffix)
+    set( blas_symbol_suffix_def "-DBLAS_FORTRAN_SUFFIX=${blas_symbol_suffix}" )
+endif()
+
 set( i 0 )
 foreach (blas_name IN LISTS blas_name_list)
     message( TRACE "i: ${i}" )
@@ -454,7 +473,7 @@ foreach (blas_name IN LISTS blas_name_list)
                 LINK_LIBRARIES
                     ${blas_libs} ${openmp_lib} # not "..." quoted; screws up OpenMP
                 COMPILE_DEFINITIONS
-                    "${mangling} ${int_size}"
+                    "${mangling} ${int_size} ${blas_symbol_suffix_def}"
                 OUTPUT_VARIABLE
                     link_output
             )
@@ -475,7 +494,7 @@ foreach (blas_name IN LISTS blas_name_list)
                 LINK_LIBRARIES
                     ${blas_libs} ${openmp_lib} # not "..." quoted; screws up OpenMP
                 COMPILE_DEFINITIONS
-                    "${mangling} ${int_size}"
+                    "${mangling} ${int_size} ${blas_symbol_suffix_def}"
                 COMPILE_OUTPUT_VARIABLE
                     compile_output
                 RUN_OUTPUT_VARIABLE
@@ -518,6 +537,9 @@ foreach (blas_name IN LISTS blas_name_list)
                 if (int_size MATCHES "[^ ]")  # non-empty
                     list( APPEND blaspp_defs_ "${int_size}" )
                 endif()
+                if (blas_symbol_suffix_def MATCHES "[^ ]")  # non-empty
+                    list( APPEND blaspp_defs_ "${blas_symbol_suffix_def}" )
+                endif()
                 if (int_size MATCHES "ILP64")
                     set( blaspp_int "int64" )
                 else()
diff --git a/config/config.h b/config/config.h
index 37b0b680..b303fb83 100644
--- a/config/config.h
+++ b/config/config.h
@@ -15,7 +15,15 @@
     #define FORTRAN_NAME( lower, UPPER ) lower
 #else
     // default is ADD_
-    #define FORTRAN_NAME( lower, UPPER ) lower ## _
+    #ifdef BLAS_FORTRAN_SUFFIX
+        // Suffix-aware variant for libraries like OpenBLAS with SYMBOLSUFFIX=64_.
+        #define FORTRAN_CONCAT_( a, b ) a##b
+        #define FORTRAN_CONCAT(  a, b ) FORTRAN_CONCAT_( a, b )
+        #define FORTRAN_NAME( lower, UPPER ) \
+            FORTRAN_CONCAT( lower##_, BLAS_FORTRAN_SUFFIX )
+    #else
+        #define FORTRAN_NAME( lower, UPPER ) lower ## _
+    #endif
 #endif
 
 //------------------------------------------------------------------------------
diff --git a/config/lapack.py b/config/lapack.py
index 057dcef3..4435793e 100644
--- a/config/lapack.py
+++ b/config/lapack.py
@@ -319,6 +319,19 @@ def blas():
     #-------------------- OpenBLAS
     if (test_openblas):
         choices.append( ['OpenBLAS', {'LIBS': '-lopenblas'}])
+        # Debian/Ubuntu ship the ILP64 build as libopenblas64, with standard
+        # (unsuffixed) dgemm_ symbols, so it needs only the -lopenblas64 name.
+        choices.append( ['OpenBLAS (ILP64, -lopenblas64)',
+                         {'LIBS': '-lopenblas64'}])
+        # OpenBLAS built with SYMBOLSUFFIX (e.g. conda-forge's libopenblas64_,
+        # exporting dgemm_64_) needs both the suffixed name and the matching
+        # BLAS_FORTRAN_SUFFIX so blaspp mangles its calls to dgemm_64_.
+        blas_symbol_suffix = config.environ['blas_symbol_suffix']
+        if (blas_symbol_suffix):
+            choices.append(
+                ['OpenBLAS (symbol suffix ' + blas_symbol_suffix + ')',
+                 {'LIBS': '-lopenblas' + blas_symbol_suffix,
+                  'CXXFLAGS': define( 'FORTRAN_SUFFIX', blas_symbol_suffix )}])
 
     #-------------------- BLIS (also used by AMD AOCL)
     if (test_blis):
diff --git a/include/blas/mangling.h b/include/blas/mangling.h
index 7e556742..fcbecece 100644
--- a/include/blas/mangling.h
+++ b/include/blas/mangling.h
@@ -14,13 +14,33 @@
 // define FORTRAN_LOWER for lowercase (IBM xlf),
 // else the default is lowercase with appended underscore
 // (GNU gcc, Intel icc, PGI pgfortan, Cray ftn).
+//
+// BLAS_FORTRAN_SUFFIX, if defined, is appended to every mangled symbol.
+// Used to link against BLAS libraries that suffix their symbols, e.g.,
+// OpenBLAS built with INTERFACE64=1 SYMBOLSUFFIX=64_ exports `dgemm_64_`.
+// Pass via CMake's `blas_symbol_suffix` option.
 #ifndef BLAS_FORTRAN_NAME
-    #if defined(BLAS_FORTRAN_UPPER)
-        #define BLAS_FORTRAN_NAME( lower, UPPER ) UPPER
-    #elif defined(BLAS_FORTRAN_LOWER)
-        #define BLAS_FORTRAN_NAME( lower, UPPER ) lower
+    #ifdef BLAS_FORTRAN_SUFFIX
+        #define BLAS_FORTRAN_CONCAT_( a, b ) a##b
+        #define BLAS_FORTRAN_CONCAT(  a, b ) BLAS_FORTRAN_CONCAT_( a, b )
+        #if defined(BLAS_FORTRAN_UPPER)
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) \
+                BLAS_FORTRAN_CONCAT( UPPER, BLAS_FORTRAN_SUFFIX )
+        #elif defined(BLAS_FORTRAN_LOWER)
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) \
+                BLAS_FORTRAN_CONCAT( lower, BLAS_FORTRAN_SUFFIX )
+        #else
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) \
+                BLAS_FORTRAN_CONCAT( lower##_, BLAS_FORTRAN_SUFFIX )
+        #endif
     #else
-        #define BLAS_FORTRAN_NAME( lower, UPPER ) lower##_
+        #if defined(BLAS_FORTRAN_UPPER)
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) UPPER
+        #elif defined(BLAS_FORTRAN_LOWER)
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) lower
+        #else
+            #define BLAS_FORTRAN_NAME( lower, UPPER ) lower##_
+        #endif
     #endif
 #endif